| 1. |
- Lozano, Rafael, et al.
(author)
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Measuring progress from 1990 to 2017 and projecting attainment to 2030 of the health-related Sustainable Development Goals for 195 countries and territories: a systematic analysis for the Global Burden of Disease Study 2017
- 2018
-
In: The Lancet. - : Elsevier. - 1474-547X .- 0140-6736. ; 392:10159, s. 2091-2138
-
Journal article (peer-reviewed)abstract
- Background: Efforts to establish the 2015 baseline and monitor early implementation of the UN Sustainable Development Goals (SDGs) highlight both great potential for and threats to improving health by 2030. To fully deliver on the SDG aim of “leaving no one behind”, it is increasingly important to examine the health-related SDGs beyond national-level estimates. As part of the Global Burden of Diseases, Injuries, and Risk Factors Study 2017 (GBD 2017), we measured progress on 41 of 52 health-related SDG indicators and estimated the health-related SDG index for 195 countries and territories for the period 1990–2017, projected indicators to 2030, and analysed global attainment. Methods: We measured progress on 41 health-related SDG indicators from 1990 to 2017, an increase of four indicators since GBD 2016 (new indicators were health worker density, sexual violence by non-intimate partners, population census status, and prevalence of physical and sexual violence [reported separately]). We also improved the measurement of several previously reported indicators. We constructed national-level estimates and, for a subset of health-related SDGs, examined indicator-level differences by sex and Socio-demographic Index (SDI) quintile. We also did subnational assessments of performance for selected countries. To construct the health-related SDG index, we transformed the value for each indicator on a scale of 0–100, with 0 as the 2·5th percentile and 100 as the 97·5th percentile of 1000 draws calculated from 1990 to 2030, and took the geometric mean of the scaled indicators by target. To generate projections through 2030, we used a forecasting framework that drew estimates from the broader GBD study and used weighted averages of indicator-specific and country-specific annualised rates of change from 1990 to 2017 to inform future estimates. We assessed attainment of indicators with defined targets in two ways: first, using mean values projected for 2030, and then using the probability of attainment in 2030 calculated from 1000 draws. We also did a global attainment analysis of the feasibility of attaining SDG targets on the basis of past trends. Using 2015 global averages of indicators with defined SDG targets, we calculated the global annualised rates of change required from 2015 to 2030 to meet these targets, and then identified in what percentiles the required global annualised rates of change fell in the distribution of country-level rates of change from 1990 to 2015. We took the mean of these global percentile values across indicators and applied the past rate of change at this mean global percentile to all health-related SDG indicators, irrespective of target definition, to estimate the equivalent 2030 global average value and percentage change from 2015 to 2030 for each indicator. Findings: The global median health-related SDG index in 2017 was 59·4 (IQR 35·4–67·3), ranging from a low of 11·6 (95% uncertainty interval 9·6–14·0) to a high of 84·9 (83·1–86·7). SDG index values in countries assessed at the subnational level varied substantially, particularly in China and India, although scores in Japan and the UK were more homogeneous. Indicators also varied by SDI quintile and sex, with males having worse outcomes than females for non-communicable disease (NCD) mortality, alcohol use, and smoking, among others. Most countries were projected to have a higher health-related SDG index in 2030 than in 2017, while country-level probabilities of attainment by 2030 varied widely by indicator. Under-5 mortality, neonatal mortality, maternal mortality ratio, and malaria indicators had the most countries with at least 95% probability of target attainment. Other indicators, including NCD mortality and suicide mortality, had no countries projected to meet corresponding SDG targets on the basis of projected mean values for 2030 but showed some probability of attainment by 2030. For some indicators, including child malnutrition, several infectious diseases, and most violence measures, the annualised rates of change required to meet SDG targets far exceeded the pace of progress achieved by any country in the recent past. We found that applying the mean global annualised rate of change to indicators without defined targets would equate to about 19% and 22% reductions in global smoking and alcohol consumption, respectively; a 47% decline in adolescent birth rates; and a more than 85% increase in health worker density per 1000 population by 2030. Interpretation: The GBD study offers a unique, robust platform for monitoring the health-related SDGs across demographic and geographic dimensions. Our findings underscore the importance of increased collection and analysis of disaggregated data and highlight where more deliberate design or targeting of interventions could accelerate progress in attaining the SDGs. Current projections show that many health-related SDG indicators, NCDs, NCD-related risks, and violence-related indicators will require a concerted shift away from what might have driven past gains—curative interventions in the case of NCDs—towards multisectoral, prevention-oriented policy action and investments to achieve SDG aims. Notably, several targets, if they are to be met by 2030, demand a pace of progress that no country has achieved in the recent past. The future is fundamentally uncertain, and no model can fully predict what breakthroughs or events might alter the course of the SDGs. What is clear is that our actions—or inaction—today will ultimately dictate how close the world, collectively, can get to leaving no one behind by 2030.
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| 2. |
- Murray, Christopher J. L., et al.
(author)
-
Population and fertility by age and sex for 195 countries and territories, 1950–2017: a systematic analysis for the Global Burden of Disease Study 2017
- 2018
-
In: The Lancet. - 1474-547X .- 0140-6736. ; 392:10159, s. 1995-2051
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Journal article (peer-reviewed)abstract
- Background: Population estimates underpin demographic and epidemiological research and are used to track progress on numerous international indicators of health and development. To date, internationally available estimates of population and fertility, although useful, have not been produced with transparent and replicable methods and do not use standardised estimates of mortality. We present single-calendar year and single-year of age estimates of fertility and population by sex with standardised and replicable methods. Methods: We estimated population in 195 locations by single year of age and single calendar year from 1950 to 2017 with standardised and replicable methods. We based the estimates on the demographic balancing equation, with inputs of fertility, mortality, population, and migration data. Fertility data came from 7817 location-years of vital registration data, 429 surveys reporting complete birth histories, and 977 surveys and censuses reporting summary birth histories. We estimated age-specific fertility rates (ASFRs; the annual number of livebirths to women of a specified age group per 1000 women in that age group) by use of spatiotemporal Gaussian process regression and used the ASFRs to estimate total fertility rates (TFRs; the average number of children a woman would bear if she survived through the end of the reproductive age span [age 10–54 years] and experienced at each age a particular set of ASFRs observed in the year of interest). Because of sparse data, fertility at ages 10–14 years and 50–54 years was estimated from data on fertility in women aged 15–19 years and 45–49 years, through use of linear regression. Age-specific mortality data came from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 estimates. Data on population came from 1257 censuses and 761 population registry location-years and were adjusted for underenumeration and age misreporting with standard demographic methods. Migration was estimated with the GBD Bayesian demographic balancing model, after incorporating information about refugee migration into the model prior. Final population estimates used the cohort-component method of population projection, with inputs of fertility, mortality, and migration data. Population uncertainty was estimated by use of out-of-sample predictive validity testing. With these data, we estimated the trends in population by age and sex and in fertility by age between 1950 and 2017 in 195 countries and territories. Findings: From 1950 to 2017, TFRs decreased by 49·4% (95% uncertainty interval [UI] 46·4–52·0). The TFR decreased from 4·7 livebirths (4·5–4·9) to 2·4 livebirths (2·2–2·5), and the ASFR of mothers aged 10–19 years decreased from 37 livebirths (34–40) to 22 livebirths (19–24) per 1000 women. Despite reductions in the TFR, the global population has been increasing by an average of 83·8 million people per year since 1985. The global population increased by 197·2% (193·3–200·8) since 1950, from 2·6 billion (2·5–2·6) to 7·6 billion (7·4–7·9) people in 2017; much of this increase was in the proportion of the global population in south Asia and sub-Saharan Africa. The global annual rate of population growth increased between 1950 and 1964, when it peaked at 2·0%; this rate then remained nearly constant until 1970 and then decreased to 1·1% in 2017. Population growth rates in the southeast Asia, east Asia, and Oceania GBD super-region decreased from 2·5% in 1963 to 0·7% in 2017, whereas in sub-Saharan Africa, population growth rates were almost at the highest reported levels ever in 2017, when they were at 2·7%. The global average age increased from 26·6 years in 1950 to 32·1 years in 2017, and the proportion of the population that is of working age (age 15–64 years) increased from 59·9% to 65·3%. At the national level, the TFR decreased in all countries and territories between 1950 and 2017; in 2017, TFRs ranged from a low of 1·0 livebirths (95% UI 0·9–1·2) in Cyprus to a high of 7·1 livebirths (6·8–7·4) in Niger. The TFR under age 25 years (TFU25; number of livebirths expected by age 25 years for a hypothetical woman who survived the age group and was exposed to current ASFRs) in 2017 ranged from 0·08 livebirths (0·07–0·09) in South Korea to 2·4 livebirths (2·2–2·6) in Niger, and the TFR over age 30 years (TFO30; number of livebirths expected for a hypothetical woman ageing from 30 to 54 years who survived the age group and was exposed to current ASFRs) ranged from a low of 0·3 livebirths (0·3–0·4) in Puerto Rico to a high of 3·1 livebirths (3·0–3·2) in Niger. TFO30 was higher than TFU25 in 145 countries and territories in 2017. 33 countries had a negative population growth rate from 2010 to 2017, most of which were located in central, eastern, and western Europe, whereas population growth rates of more than 2·0% were seen in 33 of 46 countries in sub-Saharan Africa. In 2017, less than 65% of the national population was of working age in 12 of 34 high-income countries, and less than 50% of the national population was of working age in Mali, Chad, and Niger. Interpretation: Population trends create demographic dividends and headwinds (ie, economic benefits and detriments) that affect national economies and determine national planning needs. Although TFRs are decreasing, the global population continues to grow as mortality declines, with diverse patterns at the national level and across age groups. To our knowledge, this is the first study to provide transparent and replicable estimates of population and fertility, which can be used to inform decision making and to monitor progress. Funding: Bill & Melinda Gates Foundation.
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| 3. |
- Stanaway, Jeffrey D., et al.
(author)
-
Global, regional, and national comparative risk assessment of 84 behavioural, environmental and occupational, and metabolic risks or clusters of risks for 195 countries and territories, 1990-2017: A systematic analysis for the Global Burden of Disease Study 2017
- 2018
-
In: The Lancet. - 1474-547X .- 0140-6736. ; 392:10159, s. 1923-1994
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Journal article (peer-reviewed)abstract
- Background The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 comparative risk assessment (CRA) is a comprehensive approach to risk factor quantification that offers a useful tool for synthesising evidence on risks and risk-outcome associations. With each annual GBD study, we update the GBD CRA to incorporate improved methods, new risks and risk-outcome pairs, and new data on risk exposure levels and risk- outcome associations. Methods We used the CRA framework developed for previous iterations of GBD to estimate levels and trends in exposure, attributable deaths, and attributable disability-adjusted life-years (DALYs), by age group, sex, year, and location for 84 behavioural, environmental and occupational, and metabolic risks or groups of risks from 1990 to 2017. This study included 476 risk-outcome pairs that met the GBD study criteria for convincing or probable evidence of causation. We extracted relative risk and exposure estimates from 46 749 randomised controlled trials, cohort studies, household surveys, census data, satellite data, and other sources. We used statistical models to pool data, adjust for bias, and incorporate covariates. Using the counterfactual scenario of theoretical minimum risk exposure level (TMREL), we estimated the portion of deaths and DALYs that could be attributed to a given risk. We explored the relationship between development and risk exposure by modelling the relationship between the Socio-demographic Index (SDI) and risk-weighted exposure prevalence and estimated expected levels of exposure and risk-attributable burden by SDI. Finally, we explored temporal changes in risk-attributable DALYs by decomposing those changes into six main component drivers of change as follows: (1) population growth; (2) changes in population age structures; (3) changes in exposure to environmental and occupational risks; (4) changes in exposure to behavioural risks; (5) changes in exposure to metabolic risks; and (6) changes due to all other factors, approximated as the risk-deleted death and DALY rates, where the risk-deleted rate is the rate that would be observed had we reduced the exposure levels to the TMREL for all risk factors included in GBD 2017.
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| 4. |
- Feigin, Valery L., et al.
(author)
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Global, regional, and national burden of neurological disorders, 1990–2016 : a systematic analysis for the Global Burden of Disease Study 2016
- 2019
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In: Lancet Neurology. - : Elsevier. - 1474-4422 .- 1474-4465. ; 18:5, s. 459-480
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Journal article (peer-reviewed)abstract
- Background: Neurological disorders are increasingly recognised as major causes of death and disability worldwide. The aim of this analysis from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2016 is to provide the most comprehensive and up-to-date estimates of the global, regional, and national burden from neurological disorders.Methods: We estimated prevalence, incidence, deaths, and disability-adjusted life-years (DALYs; the sum of years of life lost [YLLs] and years lived with disability [YLDs]) by age and sex for 15 neurological disorder categories (tetanus, meningitis, encephalitis, stroke, brain and other CNS cancers, traumatic brain injury, spinal cord injury, Alzheimer's disease and other dementias, Parkinson's disease, multiple sclerosis, motor neuron diseases, idiopathic epilepsy, migraine, tension-type headache, and a residual category for other less common neurological disorders) in 195 countries from 1990 to 2016. DisMod-MR 2.1, a Bayesian meta-regression tool, was the main method of estimation of prevalence and incidence, and the Cause of Death Ensemble model (CODEm) was used for mortality estimation. We quantified the contribution of 84 risks and combinations of risk to the disease estimates for the 15 neurological disorder categories using the GBD comparative risk assessment approach.Findings: Globally, in 2016, neurological disorders were the leading cause of DALYs (276 million [95% UI 247–308]) and second leading cause of deaths (9·0 million [8·8–9·4]). The absolute number of deaths and DALYs from all neurological disorders combined increased (deaths by 39% [34–44] and DALYs by 15% [9–21]) whereas their age-standardised rates decreased (deaths by 28% [26–30] and DALYs by 27% [24–31]) between 1990 and 2016. The only neurological disorders that had a decrease in rates and absolute numbers of deaths and DALYs were tetanus, meningitis, and encephalitis. The four largest contributors of neurological DALYs were stroke (42·2% [38·6–46·1]), migraine (16·3% [11·7–20·8]), Alzheimer's and other dementias (10·4% [9·0–12·1]), and meningitis (7·9% [6·6–10·4]). For the combined neurological disorders, age-standardised DALY rates were significantly higher in males than in females (male-to-female ratio 1·12 [1·05–1·20]), but migraine, multiple sclerosis, and tension-type headache were more common and caused more burden in females, with male-to-female ratios of less than 0·7. The 84 risks quantified in GBD explain less than 10% of neurological disorder DALY burdens, except stroke, for which 88·8% (86·5–90·9) of DALYs are attributable to risk factors, and to a lesser extent Alzheimer's disease and other dementias (22·3% [11·8–35·1] of DALYs are risk attributable) and idiopathic epilepsy (14·1% [10·8–17·5] of DALYs are risk attributable).Interpretation: Globally, the burden of neurological disorders, as measured by the absolute number of DALYs, continues to increase. As populations are growing and ageing, and the prevalence of major disabling neurological disorders steeply increases with age, governments will face increasing demand for treatment, rehabilitation, and support services for neurological disorders. The scarcity of established modifiable risks for most of the neurological burden demonstrates that new knowledge is required to develop effective prevention and treatment strategies.Funding: Bill & Melinda Gates Foundation.
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| 5. |
- Feigin, Valery L., et al.
(author)
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Global, regional, and national burden of stroke and its risk factors, 1990-2019 : a systematic analysis for the Global Burden of Disease Study 2019
- 2021
-
In: Lancet Neurology. - : Elsevier. - 1474-4422 .- 1474-4465. ; 20:10, s. 795-820
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Journal article (peer-reviewed)abstract
- Background Regularly updated data on stroke and its pathological types, including data on their incidence, prevalence, mortality, disability, risk factors, and epidemiological trends, are important for evidence-based stroke care planning and resource allocation. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) aims to provide a standardised and comprehensive measurement of these metrics at global, regional, and national levels. Methods We applied GBD 2019 analytical tools to calculate stroke incidence, prevalence, mortality, disability-adjusted life-years (DALYs), and the population attributable fraction (PAF) of DALYs (with corresponding 95% uncertainty intervals [UIs]) associated with 19 risk factors, for 204 countries and territories from 1990 to 2019. These estimates were provided for ischaemic stroke, intracerebral haemorrhage, subarachnoid haemorrhage, and all strokes combined, and stratified by sex, age group, and World Bank country income level. Findings In 2019, there were 12.2 million (95% UI 11.0-13.6) incident cases of stroke, 101 million (93.2-111) prevalent cases of stroke, 143 million (133-153) DALYs due to stroke, and 6.55 million (6.00-7.02) deaths from stroke. Globally, stroke remained the second-leading cause of death (11.6% [10.8-12.2] of total deaths) and the third-leading cause of death and disability combined (5.7% [5.1-6.2] of total DALYs) in 2019. From 1990 to 2019, the absolute number of incident strokes increased by 70.0% (67.0-73.0), prevalent strokes increased by 85.0% (83.0-88.0), deaths from stroke increased by 43.0% (31.0-55.0), and DALYs due to stroke increased by 32.0% (22.0-42.0). During the same period, age-standardised rates of stroke incidence decreased by 17.0% (15.0-18.0), mortality decreased by 36.0% (31.0-42.0), prevalence decreased by 6.0% (5.0-7.0), and DALYs decreased by 36.0% (31.0-42.0). However, among people younger than 70 years, prevalence rates increased by 22.0% (21.0-24.0) and incidence rates increased by 15.0% (12.0-18.0). In 2019, the age-standardised stroke-related mortality rate was 3.6 (3.5-3.8) times higher in the World Bank low-income group than in the World Bank high-income group, and the age-standardised stroke-related DALY rate was 3.7 (3.5-3.9) times higher in the low-income group than the high-income group. Ischaemic stroke constituted 62.4% of all incident strokes in 2019 (7.63 million [6.57-8.96]), while intracerebral haemorrhage constituted 27.9% (3.41 million [2.97-3.91]) and subarachnoid haemorrhage constituted 9.7% (1.18 million [1.01-1.39]). In 2019, the five leading risk factors for stroke were high systolic blood pressure (contributing to 79.6 million [67.7-90.8] DALYs or 55.5% [48.2-62.0] of total stroke DALYs), high body-mass index (34.9 million [22.3-48.6] DALYs or 24.3% [15.7-33.2]), high fasting plasma glucose (28.9 million [19.8-41.5] DALYs or 20.2% [13.8-29.1]), ambient particulate matter pollution (28.7 million [23.4-33.4] DALYs or 20.1% [16.6-23.0]), and smoking (25.3 million [22.6-28.2] DALYs or 17.6% [16.4-19.0]). Interpretation The annual number of strokes and deaths due to stroke increased substantially from 1990 to 2019, despite substantial reductions in age-standardised rates, particularly among people older than 70 years. The highest age-standardised stroke-related mortality and DALY rates were in the World Bank low-income group. The fastest-growing risk factor for stroke between 1990 and 2019 was high body-mass index. Without urgent implementation of effective primary prevention strategies, the stroke burden will probably continue to grow across the world, particularly in low-income countries.
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| 6. |
- Garmabaki, Amir, et al.
(author)
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Maintenance Optimization Using Multi-Attribute Utility Theory
- 2016
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In: Current Trends in Reliability, Availability, Maintainability and Safety. - Cham : Encyclopedia of Global Archaeology/Springer Verlag. - 9783319235967 - 9783319235974 ; , s. 13-25
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Conference paper (peer-reviewed)abstract
- Several factors such as reliability, availability, and cost may consider in the maintenance modeling. In order to develop an optimal inspection program, it is necessary to consider the simultaneous effect of above factor in the model structure. In addition, for finding the optimal maintenance interval it is necessary to make trade-offs between several factors, which may conflicting each other as well. The study comprises of mathematical formulating an optimal interval problem based on Multi-Attribute Utility Theory (MAUT). The aim of the proposed research is to develop a methodology with supporting tools for determination of optimal inspection in a maintenance planning to assure and preserve a desired level of performance measure such as reliability, availability, risk, etc. For verification and validation purposes, the proposed methodology (analysis approach) and tools (models) will be applied in a real case which given by the literature.
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| 7. |
- Garmabaki, Amir, et al.
(author)
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Reliability modeling of open source software based on adoption behavior under stochastic environment
- 2015
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In: Safety and reliability of complex engineered systems. - Boca Raton : CRC Press. - 9781138028791 ; , s. 3995-3999
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Conference paper (peer-reviewed)abstract
- In the current digitalized world, Open Source Software (OSS) methodology provides greater value to users and leads to increased revenue for the OSS companies. This paper investigates reliability modeling for OSS. Most of software reliability models proposed in literature for OSS projects are based on closed-form methodology and do not consider the properties of OSS in the model structure. This paper models the rate of adoption of volunteers to OSS using diffusion theory and considered as fault detection rate. However, the fault detection rate may vary in such a testing environment; a modified SRGM based on Itô type Stochastic Differential Equation (SDE) is proposed to describe realistic situations. The proposed model have been verified on real data sets from open source projects, as the Apache project, which has been released in the market with new features. Results show the proposed model can describe the failure process for open source software accurately.
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| 8. |
- Mokdad, Ali H., et al.
(author)
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Diabetes mellitus and chronic kidney disease in the Eastern Mediterranean Region : findings from the Global Burden of Disease 2015 study
- 2018
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In: International Journal of Public Health. - : SPRINGER BASEL AG. - 1661-8556 .- 1661-8564. ; 63, s. 177-186
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Journal article (peer-reviewed)abstract
- We used findings from the Global Burden of Disease 2015 study to update our previous publication on the burden of diabetes and chronic kidney disease due to diabetes (CKD-DM) during 1990-2015. We extracted GBD 2015 estimates for prevalence, mortality, and disability-adjusted life years (DALYs) of diabetes (including burden of low vision due to diabetes, neuropathy, and amputations and CKD-DM for 22 countries of the EMR from the GBD visualization tools. In 2015, 135,230 (95% UI 123,034-148,184) individuals died from diabetes and 16,470 (95% UI 13,977-18,961) from CKD-DM, 216 and 179% increases, respectively, compared to 1990. The total number of people with diabetes was 42.3 million (95% UI 38.6-46.4 million) in 2015. DALY rates of diabetes in 2015 were significantly higher than the expected rates based on Socio-demographic Index (SDI). Our study showed a large and increasing burden of diabetes in the region. There is an urgency in dealing with diabetes and its consequences, and these efforts should be at the forefront of health prevention and promotion.
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| 9. |
- Ahmadi, Alireza
(author)
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Aircraft scheduled maintenance programme development : decision support methodologies and tools
- 2010
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Doctoral thesis (other academic/artistic)abstract
- The air transport business is large in its operations, integrated, automated and complex. Air carriers are constantly striving to achieve high standards of safety and simultaneously to attain an increased level of availability performance at minimal cost. This needs to be supported through an effective maintenance programme which has a major impact on the availability performance and which ultimately can enhance the aircraft’s capability to meet market demands at the lowest possible cost. The development of a maintenance programme is challenging, but can be enhanced by supporting methodologies and tools. The purpose of this study is to develop decision support methodologies and tools for aircraft scheduled maintenance programme development within the framework of Maintenance Review Board (MRB) process. To achieve the purpose of the research, literature studies, case studies, and simulations have been conducted. Empirical data have been collected through document studies, interviews, questionnaires, and observations from the aviation industry. For data analysis, theories and methodologies within risk, dependability and decision making have been combined with the best practices from the aviation industry. One result of the research is the identification of potential areas for improving the use of MSG-3 methodology in aircraft scheduled maintenance development. Another result is the development of a systematic methodology guided by the application of an Event Tree Analysis (ETA) for the identification and quantification of different operational risks caused by aircraft system failures, to support decision making for maintenance task development. A third result is a proposed methodology, based on a combination of different Multi-Criteria Decision Making (MCDM) methodologies, for selecting the most effective maintenance strategy for aircraft scheduled maintenance development. Finally, the fourth result is a proposed Cost Rate Function (CRF) model supported by a graphical approach. The approach can be used to identify the optimum maintenance interval and frequencies of Failure Finding Inspection (FFI) and to develop a combination of FFI and restoration tasks for the aircraft’s repairable items which are experiencing aging. These results are related to some of the specific industrial challenges, and are expected to enhance the capability of making effective and efficient decisions during the development of maintenance tasks. The results have been verified through interaction with experienced practitioners within major aviation manufacturers and air operators.
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| 10. |
- Ahmadi, Alireza
(author)
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An assessment of operational consequences of failures to support aircraft scheduled maintenance program development
- 2007
-
Licentiate thesis (other academic/artistic)abstract
- A majority of the direct and indirect maintenance costs in the life cycle of aircraft stems from the consequences of decisions taken during the initial maintenance program development. In particular, the preventive and corrective maintenance requirements, which greatly influence both the system availability and life cycle cost, need to be defined in order to perform only those preventive actions that are absolutely necessary and costeffective. Reliability-Centered Maintenance (RCM) is a systematic methodology used to identify the preventive maintenance tasks that are necessary to realize the inherent reliability of equipment at the lowest possible cost. Developing a scheduled maintenance program by means of RCM consists of identifying those preventive tasks which are both applicable (technically feasible) and effective (worth doing). An applicable maintenance task must satisfy the requirements of the type of failure to restore the item's initial performance capability. To be effective, a preventive maintenance task must lead to a reduced risk (or expected loss) of the consequence classes to a level which is acceptable to the user. In the design development phase, in order to identify the most cost effective solution, a design trade-off study is needed. This involves choosing the correct balance of the cost of consequences of failure and its correction, with their cost of prevention. However, during initial aircraft maintenance program development, lack of a methodology that supports the assessment of the operational consequences of failures has made the costeffectiveness analysis of maintenance tasks a challenging issue. This might reduce the accuracy of the analysis, which results in higher maintenance costs and may decreases the punctuality of operation, which ultimately increases the total aircraft life cycle cost. The purpose of this study is to develop a methodology for identifying different operational consequences and associated costs caused by aircraft system failure, in order to facilitate and enhance the capability of taking correct and efficient decisions when analyzing the cost-effectiveness of maintenance tasks. Some empirical studies of possible scenarios involving aircraft failures and their operational consequences for a commercial airline have been performed. Empirical data were extracted through document studies and interviews, guided by the application of an Event Tree Analysis (ETA). The analysis was performed together with experienced practitioners from both an aircraft manufacturer and commercial airlines, which contributed to a continuous verification of the outcomes of the study. Finally, the study has also estimated the associated cost of the identified operational consequences of failures. In order to quantify the operational consequences of failures, in the absence of adequate and reliable data, a methodology using pair-wise comparison technique has been applied to extract judgments of experts efficiently
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| 11. |
- Ahmadi, Alireza, et al.
(author)
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An overview of trends in aircraft maintenance program development : past, present, and future
- 2007
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In: Risk, Reliability and Societal Safety. - London : Taylor and Francis Group. - 9780415447867 ; , s. 2067-2076
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Conference paper (peer-reviewed)abstract
- The purpose of this paper is to describe the trends in aircraft maintenance program development during the last 50 years, including the reasons for the aircraft industry to change its view of maintenance. The major milestones and fundamental reasons for such development are also discussed and illustrated in relation to a flow diagram, which shows the logical and chronological order of the trends. Finally, the paper describes some possibilities and challenges as regards applying Information & Communication Technology (ICT) within the emerging approach of e-Maintenance in order to enhance the surveillance of aircraft maintenance program performance.
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| 12. |
- Ahmadi, Alireza, et al.
(author)
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Assessment of the cost of operational consequences of failures in aircraft operation
- 2007
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In: Proceedings of 3rd International Conference on Reliability and Safety.
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Conference paper (peer-reviewed)abstract
- Maintenance decisions regarding aircraft require consideration of the operational impact of failures. The cost of the operational impact of failure is difficult to assess due to the influence of a large number of contributory factors. This study attempts to assess the cost of operational consequences of failures using the expertise of the field experts following a pairwise contribution technique. The study shows that the proposed model can be a tool to assess the cost of operational consequences of failures in aircraft operation, when there is not sufficient and reliable data
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| 13. |
- Ahmadi, Alireza, et al.
(author)
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Assessment of the operational consequences of aircraft failures : using event tree analysis
- 2008
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In: 2008 IEEE Aerospace Conference. - Piscataway, NJ : IEEE Communications Society. - 9781424414871 ; , s. 1-14
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Conference paper (peer-reviewed)abstract
- The purpose of this paper is to describe a methodology that supports an assessment of the operational consequences of failures in aircraft systems and its associated costs, in order to facilitate a correct and efficient decision-making during cost-effectiveness analysis of maintenance tasks within scheduled aircraft maintenance program development. The paper is based on empirical studies of possible scenarios from aircraft failure to operational consequences in commercial airlines. Empirical data was extracted through document studies and interviews, guided by the application of an Event Tree Analysis (ETA). The analysis was performed together with experienced practitioners from both an aircraft manufacturer and commercial airlines, which contributed to a continuous verification of the outcomes of the study. The proposed methodology, which is based on ETA, is considered as a valuable support in the assessment of the operational consequences of failures within a MSG-3 framework. The proposed methodology focuses on assessing the operational consequences of failures and associated economical losses. Hence, in order to enable an estimation of the maintenance tasks' cost-effectiveness, the methodology should be further developed to include a cost assessment of the applicable maintenance tasks. The proposed methodology could be adapted as a support to those involved in the development of aircraft maintenance program. The operational consequences and the probabilities of the proposed event tree can be quantified by the aid of historical data or expert judgment.
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| 14. |
- Ahmadi, Alireza, et al.
(author)
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Cost based risk analysis to identify inspection and restoration intervals of hidden failures subject to aging
- 2011
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In: IEEE Transactions on Reliability. - 0018-9529 .- 1558-1721. ; 60:1, s. 197-209
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Journal article (peer-reviewed)abstract
- The analytical model presented in this paper aims to study possible maintenance strategies considering risk constrains, to preserve or assure availability of hidden functions of a repairable unit in aircraft systems considering ageing effect. The paper discusses two known strategies for hidden failure management aviation and other high risk industries, namely Failure Finding Inspection (FFI), and a combination of a series of FFI and restoration after a specific number of FFI cycles ( i.e., FFI-Rs strategy). Based on discussions, the paper introduces a new approach named Dynamic Failure Finding Inspection strategy (DFFI) to assure the acceptable level of risk and also the unit's hidden function availability continuously . The paper presents analytical methods to estimate optimal FFI, and optimal thresholds for restoration of degradation (refreshing risk level) within FFI-Rs strategy. It also discusses criteria used to select appropriate thresholds to change the FFI intervals within DFFI strategy, i.e. reducing inspection intervals after specific thresholds, to reduce the risk. The method is based on the mean proportion of time i.e. (Mean Functional Dead Time, MFDT) that the unit is not functioning during the inspection intervals and the average unavailability behavior within the restoration/discard period. The proposed method considers inspection, repair, and restoration times, and takes in to account costs associated with inspection, repair, restoration, potential losses due to non-availability of aircraft due to maintenance downtime or accident often caused multiple failures.
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| 15. |
- Ahmadi, Alireza
(author)
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Discrete element technique for modeling high-speed railway tracks
- 2023
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Licentiate thesis (other academic/artistic)abstract
- The Discrete element method (DEM) is a methodology to investigatethe interactions among granular materials. It analyzes the behavior of par-ticulate environments by solving force-displacement equations that adhereto Newton’s second law of motion. Despite its usefulness, the DEM is notwithout limitations, and researchers are still facing certain challenges thatrestrict them from performing detailed analyses of granular materials. Thisstudy addresses two issues in DEM modeling of granular materials in rail-way embankments. Firstly, the long computational time required by theDEM for modeling fine angular particles in granular materials is addressedby exploring the effects of particle scaling on the shear behavior of granularmaterial. This study investigates the impact of particle size distribution,particle angularity, and the amount of scaling on the accuracy and compu-tational efficiency of DEM. Secondly, the limitations of DEM in includingthe continuous rail beam structure in the track are addressed by verifyinga DEM model against physical measurements of a full-scale ballasted trackand investigating the influence of including the rail beam structure on high-speed railway ballasted tracks. The results show that the use of particlescaling in the first study significantly improves the computational efficiencyof the DEM while maintaining accuracy, and this method is used in thesecond study to investigate the influence of the rail beam structure on thebehavior of railway tracks.
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| 16. |
- Ahmadi, Alireza
(author)
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Epidemiology, risk and protective factors of self-immolation : a study from Iran
- 2013
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Doctoral thesis (other academic/artistic)abstract
- Background: Suicide by self-burning (self-immolation) is one of the suicide methods that is far more common in low-middle income countries than in high-income ones. Iran is one of the countries that has a high rate of self-immolation. Women are the main victims as the reports show. In this study we aim to find the epidemiology, risk and protective factors of self-immolation. Methods: Initially, we analyzed two national databases to identify the epidemiological aspects of self-immolation including demographic, geographic, cultural, economic and health-related characteristics of fatal self-immolation cases that may vary across regions of Iran (sub-study I). Subsequently, we conducted two case–control studies in regard to attempted self-immolation. One titled Preliminary study with 60 participants (30 cases and 30 controls), and the other entitled Main study with 151 cases and 302 controls dedicated to identifying the risks and protective factors of self-immolation (sub-study II-IV). Results: Results show that the total rate of suicide by all methods in Iran was 6.42 per 100,000, of which 1.74 per 100,000 (27%) were self-immolation. Seventy one percent of the self-immolators were female and the mean age was 29 years. The geographical features of self-immolation indicate that self-immolation rates are higher in the border provinces of the country, in the rural areas, and in the provinces that were most intensively affected by the postwar socioeconomic consequences, as well as Kurdish people. Results from our studies show that adjustment disorders, opium dependence, major depression, and an individual history of suicide attempts were risk factors. In the married subgroup, marital conflict and addiction of spouse and in unmarried subgroup, problems with parents, parents’ death and parents’ addiction were identified as risk factors. Moreover, "receiving consultation services" and "anxiety about school/ university performance" played protective roles against self-immolation. Regarding identification of potential factors for future prevention interventions, descriptive analyses revealed that the means of self-immolation in more than 93% of patients was kerosene. Imitational self-immolation was showed in most of self-immolation cases (more than 60%). The majority of participants (both cases and control) had not used any "consulting services" to solve or manage their problems or enhance their problem-solving abilities. Moreover, unplanned (impulsive) self-immolation was detected in 80% of all self-immolation patients Conclusion: Overall, in this study we found that self-immolation is an important public health issue in particular regions in Iran. Our results also suggest that self-immolation is a compound phenomenon with multiple potential causes. Our results have implications for interventions that aim at screening, identification, and education of individuals who are at-risk for self-immolation to reduce the rate of self-immolation in the study area.
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| 17. |
- Ahmadi, Alireza, et al.
(author)
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Estimation of economic consequences of aircraft system failures
- 2012
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In: Communications in Dependability and Quality Management. - 1450-7196. ; 15:1, s. 39-49
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Journal article (peer-reviewed)abstract
- A large portion of the direct and indirect aircraft operational costs stems from the consequences of decisions made during the maintenance program development. Decision on maintenance task selection for non-safety category of failures, is based on the cost effectiveness, in which the cost of preventive maintenance should be less than the costs associated with the corrective action and failure consequence. Although the assessment of the direct cost for preventive and corrective maintenance is quiet straightforward, however quantification and estimation of the cost associated with the consequence of failure is a great challenge. This is due to a long list of contributory factors and lack of adequate data regarding the cost headings. This study attempts to estimate the economic consequences of aircraft system failures which lead to a technical delay. The paper considers financial losses, mostly due to the additional unexpected costs related to the flight crew, passengers, aircraft itself, ramp and airport, when one of the cost headings, e.g. the pre-fixed crew cost is known. The experience of the field experts has been used following a pairwise comparison technique to compare the cost headings, and to estimate the contribution of each one to the total cost of a delay. The study shows that the proposed model can be a tool to assess the cost of failure consequences in aircraft operation, when there is a limited data and information regarding the cost headings.
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| 18. |
- Ahmadi, Alireza, et al.
(author)
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Inspection Optimization under imperfect maintenance performance
- 2017
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In: Proceedings of MPMM 2016. - Luleå : Luleå tekniska universitet. - 9789175838410 ; , s. 139-
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Conference paper (peer-reviewed)abstract
- Scheduled maintenance and inspection development is one of the main requirements for emergency equipment and safety devices. These types of devices have hidden functions which are used intermittently or infrequently, so their failure will not be evident to the operating crew. The analytical model presented in this paper deals with the periodically tested units with overhauls (preventive maintenance) after certain number of inspections and a renewal after a series of overhauls. The cost based optimization method presented in this paper identifies the optimum interval and frequency of Failure Finding Inspection (FFI) and restoration. In the proposed model, repair due to failures found by inspection makes the unit As Bad As Old, and restoration/overhaul action rejuvenates the unit to any condition between As Good As New and As Bad As Old. As Good As New effectiveness also is considered for renewal action. It considers inspection and repair times, and takes into account the costs associated with inspection, repair, restoration, and also the cost of accidents due to the occurrence of multiple failure. The results show that when the unit is not under aging process, the optimal alternative for each inspection interval is the one with highest possible number of inspection without restoration. Finally, it is observed that when the cost of accident is quite high it is needed to perform inspections at smaller intervals to control the risk of accident.
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| 19. |
- Ahmadi, Alireza, et al.
(author)
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Integration of RCM and PHM for the next generation of aircraft
- 2009
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In: 2009 IEEE Aerospace Conference. - Piscataway, NJ : IEEE Communications Society. - 9781424426218
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Conference paper (peer-reviewed)abstract
- With global cuts in defense budgets, air forces have to sustain the same level of readiness with a reduced number of aircraft. To succeed with this challenge, it is not sufficient to improve current maintenance concepts, but new ones also have to be introduced.Traditionally, the development of on-board functions and maintenance concepts has been performed rather independently. The new approach is to focus on an integration of these two developments and to adapt a life cycle view together with a disregard of organizational boundaries.To facilitate the necessary change, a study is performed by Saab and Luleå University of Technology. The study focuses on the possibilities to integrate RCM and PHM in a cost-effective way. The aim is to reduce the workload of maintenance development and to find out how to combine RCM and PHM to achieve a joint development of the aircraft and its maintenance program throughout the aircraft's whole life cycle.The paper describes some similarities and differences between RCM and PHM. Furthermore, the paper describes some aspects of how RCM and PHM are complementing each other and what kind of adaptations that has to be done to achieve a successful integration. For example, a good application of RCM early in system design might generate a pull for PHM-technology integration and motivate design changes of the aircraft. Simultaneously, available PHM-technologies might strongly affect the selection of applicable and effective maintenance tasks in the development of the initial maintenance program. PHM might also support a surveillance of the maintenance program's performance. The description is highlighted with examples and experiences from the Swedish Gripen fighter aircraft. Finally, the paper also outlines some suggestions for further research.
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| 20. |
- Ahmadi, Alireza, et al.
(author)
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On aircraft scheduled maintenance program development
- 2010
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In: Journal of Quality in Maintenance Engineering. - : Emerald. - 1355-2511 .- 1758-7832. ; 16:3, s. 229-255
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Journal article (peer-reviewed)abstract
- Purpose – The purpose of this paper is to present issues and challenges of scheduled maintenance task development within the maintenance review board (MRB) process, and to find potential areas of improvement in the application of the MSG-3 methodology for aircraft systems. Design/methodology/approach – The issues and challenges as well as potential areas of improvement have been identified through a constructive review that consists of two parts. The first part is a benchmarking between the Maintenance Steering Group (MSG-3) methodology and other established and documented versions of reliability-centred maintenance (RCM). This benchmarking focuses on the MSG-3 methodology and compares it with some RCM standards to identify differences and thereby find ways to facilitate the application of MSG-3. The second part includes a discussion about methodologies and tools that can support different steps of the MSG-3 methodology within the framework of the MRB process. Findings – The MSG-3 methodology is closely related to the RCM methodology, in which the anticipated consequences of failure are considered for risk evaluation. However, MSG-3 considers neither environmental effects of failures nor operational consequences of hidden failures. Furthermore, in MSG-3, the operational check (failure-finding inspection) is given priority before all other tasks, whereas in RCM it is considered as a default action, where there is no other applicable and effective option. While RCM allows cost-effectiveness analysis for all failures that have no safety consequences, MSG-3 just allows it for failures with economic consequences. A maintenance program that is established through the MRB process fulfils the requirements of continuous airworthiness, but there is no foundation to claim that it is the optimal or the most effective program from an operator’s point-of-view. The major challenge when striving to achieve a more effective maintenance program within the MRB process is to acquire supporting methodologies and tools for adequate risk analysis, for optimal interval assignments, and for selection of the most effective maintenance task. Originality/value – The paper presents a critical review of existing aircraft scheduled maintenance program development methodologies, and demonstrates the differences between MSG-3 and other RCM methodologies.
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| 21. |
- Ahmadi, Alireza, et al.
(author)
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Optimum Failure Finding Inspection During Extended Operation Life
- 2013
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Conference paper (peer-reviewed)abstract
- In a complex system such as railway and aviation equipment’s, it may be necessary to employ a combination of Failure Finding Inspection (FFI) and a scheduled discard task, as suggested by Reliability-Centered Maintenance (RCM). This strategy ensures an adequate level of availability of hidden functions, as well as the reduction of the risk of multiple failures to an acceptable level. However, in some situations, operators prefer to extend the discard life of components beyond their recommended life limit, due to the operational restrictions. This necessitates the definition of an optimal Failure Finding Inspection interval for the extended life period. This paper aims to provide a mathematical model for defining optimal FFI interval, during the extended period of the replacement life. A cost function (CF) is developed to identify the cost per unit of time associated with different FFI intervals, for the proposed extended period of life, i.e. postponement period. The proposed method concerns as-bad-as-old (ABAO) inspection and repairs (due to failures found by inspection). It considers inspection and repair times, and takes into account the costs associated with inspection and repair, the opportunity cost of lost production due to maintenance downtime created by inspection and repair actions, and also the cost of accidents due to the occurrence of multiple failure
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| 22. |
- Ahmadi, Alireza, et al.
(author)
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Optimum failure management strategy for periodically inspected units with imperfect maintenance
- 2016
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In: IFAC-PapersOnLine. - : Elsevier BV. - 2405-8963. ; 49:12, s. 799-804
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Journal article (peer-reviewed)abstract
- The aim of this paper is to develop a reliability-based cost model for periodically inspected units subject to hidden functions, with imperfect restoration (overhaul) action after a certain number of inspections. In the model, effectiveness of the consecutive restoration actions is considered, and possible alternative maintenance strategies are identified and compared. The method is based on the Total Cost and identifies the optimum interval and frequency of inspections, as well as restoration that minimize the total life cycle cost. In the proposed model, repair due to failures found by inspection is considered as minimal repair, and restoration/overhaul action is considered as normal repair. The result also shows that for a specific value of restoration effectiveness (θ0), when θ> θ0, the behavior of alternatives tends to as-bad-as-old and for θ< θ0 tends to an as-good-as-new. It is also observed that when the cost of accident is high it is needed to perform inspections at smaller intervals.
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| 23. |
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| 24. |
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| 25. |
- Ahmadi, Alireza, et al.
(author)
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Prerequisites for a business-oriented fleet availability assurance program in aviation
- 2010
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In: Proceedings of the 1st international workshop and congress on eMaintenance. - Luleå : Luleå tekniska universitet. ; , s. 168-175
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Conference paper (peer-reviewed)abstract
- The air transport business is a large, integrated, automated and complex domain with high requirements on safety, security and dependability. In order to achieve customer satisfaction and gain a global competitive advantage, provision of services is essential. In air transport business with an extensive competition, the consequences of unreliable services become more critical which may increase cost of operation and reduce productivity. Furthermore, occurrence of unreliable services might also lead to annoyance, inconvenience and a lasting customer dissatisfaction that can create serious problem with regarding the responsible company‟s marketplace position. Hence, it is crucial for air transport companies to continuously improve the quality of the services they provide to customer. In the context of air transport, maintenance process and maintenance-related services have a high impact on effectiveness, productivity and costs. Maintenance departments are required to ensure that their fleet is expected to meet, or continues to meet, airline‟s established availability performance goals (e.g. operational readiness, dispatch reliability and cost affectivity) and to ensure that demands for deliveries will met. One way to align maintenance decisions and business objectives and at the same time highlight where the potential weakness in the systems and maintenance performance can be expected, is through Fleet Availability Assurance Program (FAAP). However, an effective implementation of FAAP needs adaptation to the usage context. Hence, the purpose of this paper is to present an availability assurance program in airline industries, in which the essential functional elements of such a program are discussed. The paper also proposes an integrated information logistic infrastructure for this management system.
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