| 1. |
- Nambiar, Sanjay, 1997-
(författare)
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Adaptive Automation for Customized Products
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In today’s fast-paced industrial landscape, the drive for greater efficiency and flexibility in product development has sparked significant interest in innovative automation technologies. This thesis explores the usefulness of various automation techniques for customized products such as Knowledge-Based Engineering (KBE), Multidisciplinary Optimization (MDO) and machine learning frameworks.The research begins by establishing an automated framework for fixture design, combining design automation and MDO to streamline the design process. It then moves to optimizing gas turbines, introducing an automation framework that merges CAD templates with KBE principles.For complex and unstructured production, this thesis explores the use of Reinforcement Learning (RL) to tackle challenges in unstructured manufacturing. By utilizing lightweight physics-based engines and RL, the research advances automated assembly validation and mobile robot operations, pushing the boundaries of adaptive production automation. Furthermore, a framework is developed, which integrates smoothly with industrial robotic platforms showcases practical automation solutions and highlights the adaptability and applicability of digital twin technology in real-world situations.This thesis contributes to the field of product development by providing innovative solutions that are rooted in multidisciplinary research. It bridges the theoretical and practical aspects of automation with solutions that overcomes the obstacles to realize seamless integration between digital and physical realities in a manufacturing context.
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| 2. |
- Sundström, Johan, Professor, 1971-, et al.
(författare)
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Risk factors for subarachnoid haemorrhage : a nationwide cohort of 950 000 adults
- 2019
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Ingår i: International Journal of Epidemiology. - : Oxford University Press. - 0300-5771 .- 1464-3685. ; 48:6, s. 2018-2025
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Subarachnoid haemorrhage (SAH) is a devastating disease, with high mortality rate and substantial disability among survivors. Its causes are poorly understood. We aimed to investigate risk factors for SAH using a novel nationwide cohort consortium.METHODS: We obtained individual participant data of 949 683 persons (330 334 women) between 25 and 90 years old, with no history of SAH at baseline, from 21 population-based cohorts. Outcomes were obtained from the Swedish Patient and Causes of Death Registries.RESULTS: During 13 704 959 person-years of follow-up, 2659 cases of first-ever fatal or non-fatal SAH occurred, with an age-standardized incidence rate of 9.0 [95% confidence interval (CI) (7.4-10.6)/100 000 person-years] in men and 13.8 [(11.4-16.2)/100 000 person-years] in women. The incidence rate increased exponentially with higher age. In multivariable-adjusted Poisson models, marked sex interactions for current smoking and body mass index (BMI) were observed. Current smoking conferred a rate ratio (RR) of 2.24 (95% CI 1.95-2.57) in women and 1.62 (1.47-1.79) in men. One standard deviation higher BMI was associated with an RR of 0.86 (0.81-0.92) in women and 1.02 (0.96-1.08) in men. Higher blood pressure and lower education level were also associated with higher risk of SAH.CONCLUSIONS: The risk of SAH is 45% higher in women than in men, with substantial sex differences in risk factor strengths. In particular, a markedly stronger adverse effect of smoking in women may motivate targeted public health initiatives.
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| 3. |
- Bjermo, Jonas, 1977-
(författare)
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Test Design for Mean Ability Growth and Optimal Item Calibration for Achievement Tests
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, we examine two topics in the area of educational measurement. The first topic studies how to best design two achievement tests with common items such that a population mean-ability growth is measured as precisely as possible. The second examines how to calibrate newly developed test items optimally. These topics are two optimal design problems in achievement testing. Paper I consist of a simulation study where different item difficulty allocations are compared regarding the precision of mean ability growth when controlling for estimation method and item difficulty span. We take a more theoretical approach on how to allocate the item difficulties in Paper II. We use particle swarm optimization on a multi-objective weighted sum to determine an exact design of the two tests with common items. The outcome relies on asymptotic results of the test information function. The general conclusion of both papers is that we should allocate the common items in the middle of the difficulty span, with the two separate test items on different sides. When we decrease the difference in mean ability between the groups, the ranges of the common and test items coincide more.In the second part, we examine how to apply an existing optimal calibration method and algorithm using data from the Swedish Scholastic Aptitude Test (SweSAT). We further develop it to consider uncertainty in the examinees' ability estimates. Paper III compares the optimal calibration method with random allocation of items to examinees in a simulation study using different measures. In most cases, the optimal design method estimates the calibration items more efficiently. Also, we can identify for what kind of items the method works worse.The method applied in Paper III assumes that the estimated abilities are the true ones. In Paper IV, we further develop the method to handle uncertainty in the ability estimates which are based on an operational test. We examine the asymptotic result and compare it to the case of known abilities. The optimal design using estimates approaches the optimal design assuming true abilities for increasing information from the operational test.
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| 4. |
- Häggström, Jenny, 1980-
(författare)
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Selection of smoothing parameters with application in causal inference
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is a contribution to the research area concerned with selection of smoothing parameters in the framework of nonparametric and semiparametric regression. Selection of smoothing parameters is one of the most important issues in this framework and the choice can heavily influence subsequent results. A nonparametric or semiparametric approach is often desirable when large datasets are available since this allow us to make fewer and weaker assumptions as opposed to what is needed in a parametric approach. In the first paper we consider smoothing parameter selection in nonparametric regression when the purpose is to accurately predict future or unobserved data. We study the use of accumulated prediction errors and make comparisons to leave-one-out cross-validation which is widely used by practitioners. In the second paper a general semiparametric additive model is considered and the focus is on selection of smoothing parameters when optimal estimation of some specific parameter is of interest. We introduce a double smoothing estimator of a mean squared error and propose to select smoothing parameters by minimizing this estimator. Our approach is compared with existing methods.The third paper is concerned with the selection of smoothing parameters optimal for estimating average treatment effects defined within the potential outcome framework. For this estimation problem we propose double smoothing methods similar to the method proposed in the second paper. Theoretical properties of the proposed methods are derived and comparisons with existing methods are made by simulations.In the last paper we apply our results from the third paper by using a double smoothing method for selecting smoothing parameters when estimating average treatment effects on the treated. We estimate the effect on BMI of divorcing in middle age. Rich data on socioeconomic conditions, health and lifestyle from Swedish longitudinal registers is used.
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| 5. |
- Laukaityte, Inga, 1980-
(författare)
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Statistical modeling in international large-scale assessments
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contributes to the area of research based on large-scale educational assessments, focusing on the application of multilevel models. The role of sampling weights, plausible values (response variable imputed multiple times) and imputation methods are demonstrated by simulations and applications to TIMSS (Trends in International Mathematics and Science Study) and PISA (Programme for International Student Assessment) data.The large-scale assessments use multistage sampling design, which means that the units such as schools, classrooms, or students at some or all stages are selected with unequal probabilities. In order to make valid estimates and inferences sampling weights should be used. Thus, in the first paper, we examine different approaches and give recommendations concerning handling sampling weights in multilevel models when analyzing large-scale assessments.Due to limitations in time and the number of students, the complex surveys use matrix sampling of items. This means that a response variable, i.e. students' performance, contains a large amount of information that is missing by design. Therefore, in order to estimate students' proficiency, TIMSS and PISA use the plausible values approach, which results in a set of five plausible values – proficiencies, computed for each student. In the second paper, different user strategies concerning plausible values for multilevel models as well as means and variances are examined with both real and simulated data. Missing information that is present because of the matrix sampling design for instance like the one used in PISA, can be arranged into a non-monotone missing data pattern, where all variables are incomplete and highly positively correlated. In the third paper, we compare a few imputation methods: a single imputation from a conditional distribution (with and without weights) and multiple imputation, for data with a non-monotone missing pattern (with no complete variables) and high positive correlation between variables.In several of the recent international large-scale assessments, students in Sweden demonstrate a decreasing performance. Some previous research has shown that changes in performance depend on students’ performance levels. In the fourth paper, we studied the relationship between student performance and the between-school variance and tried to identify factors associated with student performance in mathematics in PISA in low-, medium-, and high- performing schools in the Nordic countries.
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| 6. |
- Lindvall, Jannika
(författare)
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Critical features and impacts of mathematics teacher professional development programs : Comparing and characterizing programs implemented at scale
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis is to contribute to the knowledge base on conceptualizations and impacts of teacher professional development (PD) programs. This is done by studying the case of two large-scale teacher PD programs. The first was mandatory for all public elementary school mathematics teachers in a larger Swedish municipality, and the second has been completed by 76% of all elementary school mathematics teachers in Sweden. In the municipality, and during the time frame in which this study was conducted, it was possible to make a comparison between teachers participating in different programs. Data on the programs’ impacts on teachers, instruction, and student achievement were gathered both immediately and one year after the teachers’ participation in one of them. In other words, the context of the study created an opportunity to respond to recent calls for studies that (a) examine the impacts of PD programs implemented on a larger scale, (b) adhere to PD programs’ impacts on teachers, instruction, and student achievement, (c) examine the sustainability of PD programs’ impacts, and (d) attend to variations within and between PD programs’ impacts. The results show that the studied programs are highly similar if characterized according to established research frameworks on what constitutes critical features of teacher PD. At the same time, they demonstrate different impacts, both between the programs and within them. These results suggested an elaboration of two of the five critical features of teacher PD: Content Focus and Coherence. Through the development and application of a more finely grained tool to characterize the programs’ Content Focus, differences between their characteristics were detected. Together with a systematic review of the PD research literature on Coherence, these results formed a basis for discussing plausible reasons for the difference in the programs’ impacts as well as elaborating on the critical features of Content Focus and Coherence. In summary, the thesis contributes: (a) empirical results in relation to large-scale teacher PD programs’ impacts; (b) methodological results in the form of tools for characterizing PD programs’ Content Focus and Coherence; and (c) theoretical results, as it examines established frameworks for characterizing teacher PD programs by using them in practice and, in light of the results, also suggests an elaboration of them.
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| 7. |
- Luo, Hao, 1984-
(författare)
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Some Aspects on Confirmatory Factor Analysis of Ordinal Variables and Generating Non-normal Data
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis, which consists of five papers, is concerned with various aspects of confirmatory factor analysis (CFA) of ordinal variables and the generation of non-normal data. The first paper studies the performances of different estimation methods used in CFA when ordinal data are encountered. To take ordinality into account the four estimation methods, i.e., maximum likelihood (ML), unweighted least squares, diagonally weighted least squares, and weighted least squares (WLS), are used in combination with polychoric correlations. The effect of model sizes and number of categories on the parameter estimates, their standard errors, and the common chi-square measure of fit when the models are both correct and misspecified are examined. The second paper focuses on the appropriate estimator of the polychoric correlation when fitting a CFA model. A non-parametric polychoric correlation coefficient based on the discrete version of Spearman's rank correlation is proposed to contend with the situation of non-normal underlying distributions. The simulation study shows the benefits of using the non-parametric polychoric correlation under conditions of non-normality. The third paper raises the issue of simultaneous factor analysis. We study the effect of pooling multi-group data on the estimation of factor loadings. Given the same factor loadings but different factor means and correlations, we investigate how much information is lost by pooling the groups together and only estimating the combined data set using the WLS method. The parameter estimates and their standard errors are compared with results obtained by multi-group analysis using ML. The fourth paper uses a Monte Carlo simulation to assess the reliability of the Fleishman's power method under various conditions of skewness, kurtosis, and sample size. Based on the generated non-normal samples, the power of D'Agostino's (1986) normality test is studied. The fifth paper extends the evaluation of algorithms to the generation of multivariate non-normal data. Apart from the requirement of generating reliable skewness and kurtosis, the generated data also need to possess the desired correlation matrices. Four algorithms are investigated in terms of simplicity, generality, and reliability of the technique.
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| 8. |
- Lyrén, Per-Erik, 1976-
(författare)
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A perfect score : Validity arguments for college admission tests
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- College admission tests are of great importance for admissions systems in general and for candidates in particular. The SweSAT (Högskoleprovet in Swedish) has been used for college admission in Sweden for more than 30 years, and today it is alongside with the upper-secondary school GPA the most widely used instrument for selection of college applicants. Because of the importance that is placed on the SweSAT, it is essential that the scores are reliable and that the interpretations and uses of the scores are valid. The main purpose of this thesis was therefore to examine some assumptions that are of importance for the validity of the interpretation and use of SweSAT scores. The argument-based approach to validation was used as the framework for the evaluation of these assumptions.The thesis consists of four papers and an extensive introduction with summaries of the papers. The first three papers examine assumptions that are relevant for the use of SweSAT scores for admission decisions, while the fourth paper examines an assumption that is relevant for the use of SweSAT scores for providing diagnostic information. The first paper is a review of predictive validity studies that have been performed on the SweSAT. The general conclusion from the review is that the predictive validity of SweSAT scores varies greatly among study programs, and that there are many problematic issues related to the methodology of the predictive validity studies. The second paper focuses on an assumption underlying the current SweSAT equating design, namely that the groups taking different forms of the test have equal abilities. The results show that this assumption is highly problematic, and consequently a more appropriate equating design should be applied when equating SweSAT scores. The third paper examines the effect of textual item revisions on item statistics and preequating outcomes, using data from the SweSAT data sufficiency subtest. The results show that most kinds of revisions have a significant effect on both p-values and point-biserial correlations, and as a consequence the preequating outcomes are affected negatively. The fourth paper examines whether there is added value in reporting subtest scores rather than just the total score to the test-takers. Using a method derived from classical test theory, the results show that all observed subscores are better predictors of the true subscores than is the observed total score, with the exception of the Swedish reading comprehension subtest. That is, the subscores contain information that the test-takers can use for remedial studies and hence there is added value in reporting the subscores. The general conclusion from the thesis as a whole is that the interpretations and use of SweSAT scores are based on several questionable assumptions, but also that the interpretations and uses are supported by a great deal of validity evidence.
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| 9. |
- Sundström, Anna, 1979-
(författare)
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Developing and validating self-report instruments : assessing perceived driver competence
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The overall aim of this thesis was to develop and validate a self-report instrument for perceived driver competence. The thesis includes six papers and a summary. All papers focus on perceived driver competence from a measurement perspective; that is, how to develop an instrument for perceived driver competence and how to use and interpret the scores from the instrument in a reliable and valid manner.Study I reviews how perceived driver competence has been measured in other studies and discusses these methods from a measurement perspective. Most studies have examined perceived driver competence by asking drivers to compare their own skill to that of the average driver. That method is problematic, since it is not possible to determine if drivers are overconfident or not, when empirical information of their own skills is missing. In order to examine if drivers overestimate their skills or not, perceived driver competence should be compared with actual driving performance.Study II reports on the development and psychometric evaluation of a self-report instrument for perceived driver competence - the Self-Efficacy Scale for Driver Competence (SSDC). The findings provides support for construct validity, as the SSDC demonstrated sound psychometric properties and as the internal structure of the SSDC corresponded to the theoretical model used as a basis for instrument development.In study III, the psychometric properties of the SSDC were further examined using an item response theory (IRT) model. The findings confirmed the results indicated by the classical analyses in Study II. Additional information was provided by the IRT analyses, as it was indicated that the scale would benefit from fewer scale points or by putting labels on each scale point.In study IV, Swedish and Finnish candidates’ self-assessment accuracy was examined by comparing candidates’ scores on the SSDC and a similar instrument for self-assessment of driving skill used in Finland, with driving test performance. Unlike previous studies, in which drivers compared their perceived skills to that of the average driver, a relatively large proportion made a realistic assessment of their own skills. In addition, in contrast to previous studies, no gender differences were found. These results were also confirmed in study V, where the results from the Finnish instrument for self-assessment of driving skill were compared with the results from a similar instrument used in the Netherlands.Study VI further examined the construct validity of a revised version of the SSDC, combining qualitative and quantitative sources of evidence. There was a strong relationship between the SSDC and an instrument for self-assessment of driving skills, providing support for convergent validity. No relationship was found between the SSDC and driving test performance. Explanations of the lack of relationship were provided from semi-structured interviews, as they indicated that confidence in performing different tasks in the test are different from being confident of passing the test, and that the candidates are familiar neither with assessing their own skills nor with the requirements for passing the test.In conclusion, the results from this thesis indicated that the choice of methods for assessing perceived driver competence as well as the quality of these methods affect the validity. The results provided support for different aspects of construct validity of the SSDC. Moreover, the findings illustrated the benefits of combining different methods in test validation, as each method contributed information about the validity of the SSDC. The studies in this thesis mainly examined internal and external aspects of construct validity. Future studies should examine procedural validity of the SSDC.
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| 10. |
- Wedman, Jonathan, 1983-
(författare)
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Theory and validity evidence for a large-scale test for selection to higher education
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Validity is a crucial part of all forms of measurement, and especially in instruments that are high-stakes to the test takers. The aim of this thesis was to examine theory and validity evidence for a recently revised large-scale instrument used for selection to higher education in Sweden, the Swedish Scholastic Assessment Test (SweSAT), as well as identify threats to its validity. Previous versions of the SweSAT have been intensely studied but when it was revised in 2011, further research was needed to strengthen the validity arguments for the test. The validity approach suggested in the most recent version of the Standards for education and psychological testing, in which the theoretical basis and five sources of validity evidence are the key aspects of validity, was adopted in this thesis.The four studies that are presented in this thesis focus on different aspects of the SweSAT, including theory, score reporting, item functioning and linking of test forms. These studies examine validity evidence from four of the five sources of validity: evidence based on test content, response processes, internal structure and consequences of testing.The results from the thesis as a whole show that there is validity evidence that supports some of the validity arguments for the intended interpretations and uses of SweSAT scores, and that there are potential threats to validity that require further attention. Empirical evidence supports the two-dimensional structure of the construct scholastic proficiency, but the construct requires a more thorough definition in order to better examine validity evidence based on content and consequences for test takers. Section scores provide more information about test takers' strengths and weaknesses than what is already provided by the total score and can therefore be reported, but subtest scores do not provide additional information and should not be reported. All four quantitative subtests, as well as the Swedish reading comprehension subtest, are essentially free of differential item functioning (DIF) but there is moderate DIF that could be bias in two of the four verbal subtests. Finally, the equating procedure, although it appears to be appropriate, needs to be examined further in order to determine whether it is the best practice available or not for the SweSAT.Some of the results in this thesis are specific to the SweSAT because only SweSAT data was used but the design of the studies and the methods that were applied serve as practical examples of validating a test and are therefore likely useful to different populations of people involved in test development, test use and psychometric research.Suggestions for further research include: (1) a study to create a more clear and elaborate definition of the construct, scholastic proficiency; (2) a large and empirically focused study of subscore value in the SweSAT using repeat test takers and applying Haberman’s method along with recently proposed effect size measures; (3) a cross-validation DIF-study using more recently administered test forms; (4) a study that examines the causes for the recurring score differences between women and men on the SweSAT; and (5) a study that re-examines the best practice for equating the current version of the SweSAT, using simulated data in addition to empirical data.
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