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| 3. |
- Berhe, Leakemariam, 1960-
(författare)
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Statistical modeling and design in forestry : The case of single tree models
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Forest quantification methods have evolved from a simple graphical approach to complex regression models with stochastic structural components. Currently, mixed effects models methodology is receiving attention in the forestry literature. However, the review work (Paper I) indicates a tendency to overlook appropriate covariance structures in the NLME modeling process.A nonlinear mixed effects modeling process is demonstrated in Paper II using Cupressus lustanica tree merchantable volume data and compared several models with and without covariance structures. For simplicity and clarity of the nonlinear mixed effects modeling, four phases of modeling were introduced. The nonlinear mixed effects model for C. lustanica tree merchantable volume with the covariance structures for both the random effects and within group errors has shown a significant improvement over the model with simplified covariance matrix. However, this statistical significance has little to explain in the prediction performance of the model.In Paper III, using several performance indicator statistics, tree taper models were compared in an effort to propose the best model for the forest management and planning purpose of the C. lustanica plantations. Kozak's (1988) tree taper model was found to be the best for estimating C. lustanica taper profile.Based on the Kozak (1988) tree taper model, a Ds optimal experimental design study is carried out in Paper IV. In this study, a Ds-optimal (sub) replication free design is suggested for the Kozak (1988) tree taper model.
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| 6. |
- Alter, George, et al.
(författare)
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The family and mortality : A case study from rural Belgium
- 2001
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Ingår i: Annales de Démographie Historique. - 0066-2062 .- 1776-2774. ; 2001, s. 11-31
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Tidskriftsartikel (refereegranskat)abstract
- Differences in mortality among families give us clues about the importance of unobserved health-related behaviors. For example, if lower mortality was due to types of personal behavior learned in childhood, it should carry over to mortality at older ages. In this paper we use records from a nineteenth-century Belgian community to look at differences at mortality differences among families in two ways. First, we construct a direct measure of exposure to disease in childhood by counting the number of children in each family that died before age 15. Second, we calculate the overall effect of inter-family differences by using a "random effect" model that estimates the variance of the "family effect". Both of these measures show a strong family effect in childhood, but this effect diminishes after age 15 and disappears after age 55. Moreover, in a period still dominated by infectious diseases, those who survived diseases in childhood acquired immunities that helped them in later life.
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| 7. |
- Arneborg, Lars, 1969, et al.
(författare)
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MIXING IN FJORDS AND THE RELATION BETWEEN LOCAL ENERGY DISSIPATION AT A FJORD SILL AND RADIATED INTERNAL TIDES
- 2012
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Ingår i: TOS/ASLO/AGU 2012 Ocean Science Meeting abstract book, Salt Lake City, USA.
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Konferensbidrag (refereegranskat)abstract
- Diapycnal mixing in a sill fjord is vital for renewal of the deep water inside the sill. Tides can cause such mixing, both by local turbulence at the sill associated with supercritical baroclinic flow and internal hydraulic jumps, and by radiation of internal tides away from the sill that dissipate elsewhere and cause turbulence and mixing there. Previous studies tend to look at these two processes as independent of each others, whereas they in reality are closely linked: The internal tide generation depends on the hydraulic conditions at the fjord sill, and the internal hydraulic jump strength depends on the upstream and downstream radiated columnar disturbances which over time constitute the internal tides. An effort is done to link the hydraulic theory and the internal tide generation theory, and the result is compared to recent intensive observations over the Oslo fjord sill, including high-resolution microstructure profiler transects and mooring data on and inside the sill.
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| 8. |
- Arneborg, Lars, 1969, et al.
(författare)
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Tidal Energy Loss, Internal Tide Radiation, and Local Dissipation for Two-Layer Tidal Flow over a Sill
- 2017
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Ingår i: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 47:7, s. 1521-1538
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Tidskriftsartikel (refereegranskat)abstract
- A simple analytical model for tidal energy loss at fjord sills and its partitioning into local dissipation and radiated internal tides is presented. The analytical model builds on a two-layer assumption with quasi-steady nonlinear flow over the sill and wave radiation in the far field. When the interface is situated above sill level, upstream-and downstream-propagating internal waves are generated as the bottom-layer flow becomes partially blocked because of a hydraulic control over the sill. When this control sets in, energy is lost in the transition from supercritical flow over the sill to subcritical flow downstream of the sill. The analytical model is compared with observations at the Drobak sill in the Oslo Fjord and with idealized numerical simulations with a nonhydrostatic primitive equation model. The overall good agreement between observations, analytical model, and numerical model results indicates that the hydraulic control over the sill is a key player for both the generation of internal tides and the local energy loss. The tidal energy loss decreases with increasing height of the interface above the sill. At the same time, the fraction of energy dissipated locally increases from about 20% for the interface situated at sill level to > 50% when the upper-layer thickness is less than about 80% of the sill depth. These results correspond well with the observations in the Oslo Fjord where more energy is dissipated near the sill than is radiated away.
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| 17. |
- Bengtsson, Tommy, et al.
(författare)
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Famines and mortality crises in 18th to 19th century southern Sweden
- 2011
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Ingår i: Genus: Journal of Population Sciences. - Rome : Università degli Studi di Roma La Sapienza. - 2035-5556. ; 67:2, s. 119-139
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Tidskriftsartikel (refereegranskat)abstract
- Causality is an important but complicated issue, not only within social sciences in general but also within economic and historical demography. Here we are dealing with two different, but related, problems of causality. The first is to what extent the impact of food prices on mortality is biased when selecting on years with mortality crises. The second concerns the problem of mixing factors that directly and indirectly have an impact on mortality. Dealing with the first problem, we compare the effects of food prices on child and adult mortality when selecting on mortality crises with a standard approach without selection. When dealing with the second problem we use the additive hazards model, in combination with dynamic path analysis, which allows for investigating the mediating effect of intermediate covariates in a causal framework. We use individual level data from the Scanian Economic Demographic Database for five rural parishes for the period 1766 to 1865. Data on food prices refers to the local area of these parishes. The statistical analyses are performed in the R statistical computing environment, especially with the aid of the package eha. The main findings are that selecting on mortality crises created a large bias in the direction of overestimating the impact of food prices and that that the direct effects of food prices are dominating.
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| 24. |
- Berglund, Sara, 1990-
(författare)
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Tracing pathways in the ocean circulation : A temperature and salinity perspective
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The ocean circulation plays an essential role in our climate system. It redistributes heat, salt, carbon and other tracers across the globe, making the climate of Earth more moderate. This thesis targets density differences that are driving the ocean circulation. These differences are caused by changes in temperature and salinity. The analysis is based on the usage of Lagrangian trajectories simulated with velocity fields from an Earth System Model. The Lagrangian approach opens up for the possibility to follow specific water paths and water masses. The results herein provide a new insight to specific circulation patterns in the ocean, and which regions that play an important role in controlling temperature and salinity changes.In the first two articles, the Lagrangian divergence is introduced. It shows the geographical distribution of heat and salt changes of a simulated water mass. Using this, we are able to show that the northward flowing water in the Atlantic Ocean cools and freshens in the North Atlantic Subtropical Gyre, the Gulf Stream and the North Atlantic Current. Similarly, we show that the water flowing from the Drake Passage, following the Antarctic Circumpolar Current (ACC) and moving northwards into the Atlantic, Pacific and Indian oceans, transforms from cold and fresh to warm and saline. This warming and salinification are a result of, not only air-sea fluxes, but also interior mixing.In the third study, we show that 70% of the water flowing northwards as part of the Atlantic Meridional Overturning Circulation circuits the North Atlantic Subtropical Gyre at least once before it continues northwards. In the gyre, the water spirals downwards as it gets denser, due to a combination of air-sea fluxes and interior mixing. These results bring a new perspective on the Subtropical Gyre's role to the circulation patterns of the Atlantic Meridional Overturning Circulation.In the last part of this thesis, the circulation in the North Atlantic Ocean is traced into four different pathways. The pathways are visualised geographically together with their change in temperature, salinity and density. With this, we are able to show that the northward flowing water in the Atlantic Ocean exchanges heat and salt with the colder and fresher waters circulating the Subpolar Gyre.
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| 25. |
- Bosi, Sofia, et al.
(författare)
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The Role of Stokes Drift in the Dispersal of North Atlantic Surface Marine Debris
- 2021
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the physical mechanisms behind the transport and accumulation of floating objects in the ocean is crucial to efficiently tackle the issue of marine pollution. The main sinks of marine plastic are the coast and the bottom sediment. This study focuses on the former, investigating the timescales of dispersal from the ocean surface and onto coastal accumulation areas through a process called "beaching. " Previous studies found that the Stokes drift can reach the same magnitude as the Eulerian current speed and that it has a long-term effect on the trajectories of floating objects. Two particle tracking models (PTMs) are carried out and then compared, one with and one without Stokes drift, named PTM-SD and PTM-REF, respectively. Eulerian velocity and Stokes drift data from global reanalysis datasets are used for particle advection. Particles in the PTM-SD model are found to beach at a yearly rate that is double the rate observed in PTM-REF. The main coastal attractors are consistent with the direction of large-scale atmospheric circulation (Westerlies and Trade Winds). After 12 years (at the end of the run), the amount of beached particles is 20% larger in PTM-SD than in PTM-REF. Long-term predictions carried out with the aid of adjacency matrices found that after 100 years all particles have beached in PTM-SD, while 8% of the all seeded particles are still floating in PTM-REF. The results confirm the need to accurately represent the Stokes drift in particle models attempting to predict the behaviour of marine debris, in order to avoid overestimation of its residence time in the ocean and effectively guide policies toward prevention and removal.
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| 26. |
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| 27. |
- Broström, Göran, et al.
(författare)
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A hazards approach to the biometric analysis of infant mortality
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A variation of the Bourgeois-Pichat biometric analysis of infant mortality is suggested. In the original model, cumulative mortality in the last eleven months of infancy is assumed to follow a uniform distribution given a log-cube transformation of age. Instead, we assume an exponential distribution. The difference is that while the denominator is constant in the Bourgeois-Pichat model, equal to the number of births, in our model, the denominator is the current population at risk. We argue that our assumption is more satisfactory from a theoretical point of view, since it focus on the conditional probability of dying. Our model gives different estimates of endogenous and exogenous mortality and, in addition, the model fit is slightly better, especially in cases with higher levels of infant mortality.
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| 28. |
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| 29. |
- Broström, Göran, 1942-
(författare)
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A modification of Fisher's omnibus test
- 1998
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Ingår i: Communications in Statistics - Theory and Methods. - 0361-0926 .- 1532-415X. ; 27, s. 2663-2674
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Tidskriftsartikel (refereegranskat)
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| 30. |
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| 31. |
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| 32. |
- Broström, Göran, et al.
(författare)
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Att läsa i Umeå är ett bra val
- 2005
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Ingår i: Västerbottens-Kuriren. ; :9 december, s. 4-
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 33. |
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| 34. |
- Broström, Göran
(författare)
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Cox regression, Ties without tears
- 2002
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Ingår i: Communications in Statistics: Theory and Methods. ; 31, s. 285-297
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Tidskriftsartikel (refereegranskat)
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| 35. |
- Broström, Göran, et al.
(författare)
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Do conditions in early life affect old-age mortality directly and indirectly? : Evidence from 19th-century rural Sweden
- 2009
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Ingår i: Social Science and Medicine. - : Elsevier. - 0277-9536 .- 1873-5347. ; 68:9, s. 1583-1590
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Tidskriftsartikel (refereegranskat)abstract
- Previous research has shown that the disease load experienced during the birth year, measured as the infant mortality rate, had a significant influence on old-age mortality in nineteenth-century rural Sweden. We know that children born in years with very high rates of infant mortality, due to outbreaks of smallpox or whooping cough, and who still survived to adulthood and married, faced a life length several years shorter than others. We do not know, however, whether this is a direct effect, caused by permanent physical damage leading to fatal outcomes later in life, or an indirect effect, via its influence on accumulation of wealth and obtained socio-economic status. The Scanian Demographic Database, with information on five rural parishes in southern Sweden between 1813 and 1894, contains the data needed to distinguish between the two mechanisms. First, the effects of conditions in childhood on obtained socio-economic status as an adult are analyzed, then the effects of both early-life conditions and socio-economic status at various stages of life on old-age mortality. By including random effects, we take into account possible dependencies in the data due to kinship and marriage. We find that a high disease load during the first year of life had a strong negative impact on a person's ability to acquire wealth, never before shown for a historical setting. This means that it is indeed possible that the effects of disease load in the first year of life indirectly affect mortality in old age through obtained socio-economic status. We find, however, no effects of obtained socio-economic status on old-age mortality. While the result is interesting per se, constituting a debatable issue, it means that the argument that early-life conditions indirectly affect old-age mortality is not supported. Instead, we find support for the conclusion that the effect of the disease load in early-life is direct or, in other words, that physiological damage from severe infections at the start of life leads to higher mortality at older ages. Taking random effects at family level into account did not alter this conclusion.
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| 36. |
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| 37. |
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| 38. |
- Broström, Göran, 1942-
(författare)
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Event history analysis with R
- 2012. - 1
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Bok (refereegranskat)abstract
- With an emphasis on social science applications, Event History Analysis with R presents an introduction to survival and event history analysis using real-life examples. Keeping mathematical details to a minimum, the book covers key topics, including both discrete and continuous time data, parametric proportional hazards, and accelerated failure times.Features:Introduces parametric proportional hazards models with baseline distributions like the Weibull, Gompertz, Lognormal, and Piecewise constant hazard distributions, in addition to traditional Cox regressionPresents mathematical details as well as technical material in an appendixIncludes real examples with applications in demography, econometrics, and epidemiologyProvides a dedicated R package, eha, containing special treatments, including making cuts in the Lexis diagram, creating communal covariates, and creating period statisticsA much-needed primer, Event History Analysis with R is a didactically excellent resource for students and practitioners of applied event history and survival analysis.
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| 39. |
- Broström, Göran
(författare)
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Event history analysis with R
- 2021. - 2
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Bok (refereegranskat)abstract
- With an emphasis on social science applications, Event History Analysis with R, Second Edition, presents an introduction to survival and event history analysis using real-life examples. Since publication of the first edition, focus in the field has gradually shifted towards the analysis of large and complex datasets. This has led to new ways of tabulating and analysing tabulated data with the same precision and power as that of an analysis of the full data set. Tabulation also makes it possible to share sensitive data with others without violating integrity.The new edition extends on the content of the first by both improving on already given methods and introducing new methods. There are two new chapters, Explanatory Variables and Regression, and Register- Based Survival Data Models. The book has been restructured to improve the flow, and there are significant updates to the computing in the supporting R package.
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| 40. |
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| 41. |
- Broström, Göran, 1942-, et al.
(författare)
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Generalized linear models with clustered data : fixed and random effects models
- 2011
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Ingår i: Computational Statistics & Data Analysis. - : Elsevier BV. - 0167-9473 .- 1872-7352. ; 55:12, s. 3123-3134
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Tidskriftsartikel (refereegranskat)abstract
- The statistical analysis of mixed effects models for binary and count data is investigated. In the statistical computing environment R, there are a few packages that estimate models of this kind. The packagelme4 is a de facto standard for mixed effects models. The packageglmmML allows non-normal distributions in the specification of random intercepts. It also allows for the estimation of a fixed effects model, assuming that all cluster intercepts are distinct fixed parameters; moreover, a bootstrapping technique is implemented to replace asymptotic analysis. The random intercepts model is fitted using a maximum likelihood estimator with adaptive Gauss–Hermite and Laplace quadrature approximations of the likelihood function. The fixed effects model is fitted through a profiling approach, which is necessary when the number of clusters is large. In a simulation study, the two approaches are compared. The fixed effects model has severe bias when the mixed effects variance is positive and the number of clusters is large.
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| 42. |
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| 43. |
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| 44. |
- Broström, Göran, et al.
(författare)
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Inheritance, Environment, and Mortality in Older Ages, Southern Sweden, 1813-1894
- 2008
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Ingår i: Kinship and Demographic Behavior in the Past. - 9781402067327 ; , s. 185-201
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Bokkapitel (refereegranskat)abstract
- This essay explores the role played by the inheritance on human longevity. We estimate a model of overall mortality among married persons aged 50 years and above taking genetic as well as socioeconomic factors into account. We consider whether these factors have temporal or long-lasting effects on health. The demographic and economic individual level data come from the Scanian Demographic Database. These data cover five rural parishes in the southernmost part of Sweden for the period 1813-1894. To these, local grain prices, as an indicator of food costs, and the local infant mortality rate, as an indicator of the disease load, have been added. We find that age of death of the mother and the father have persistent impacts on their adult children's overall mortality regardless of sex, even after controlling for socioeconomic an environmental factors throughout the life course. In addition, we find strong birth cohort effects and effects of the disease load in the first year of life on male offspring. We are, however, unable to find any effects of socioeconomic status, neither at the time of birth or achieved later in life, a result consistent with earlier findings.
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| 45. |
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| 46. |
- Broström, Göran
(författare)
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Longevity and the aging Swedish population
- 2008
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Ingår i: Population Association of America. ; , s. 4-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper is focusing, first, on the very concept of aging, what does it mean for a population, and what does it mean to an individual. Second, on the individual level, is longevity clustered within certain families (family trees)?
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| 47. |
- Broström, Göran, et al.
(författare)
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Note on Coriolis-Stokes force and energy
- 2014
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Ingår i: Ocean Dynamics. - : Springer Science and Business Media LLC. - 1616-7341 .- 1616-7228. ; 64:7, s. 1039-1045
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we consider the origin of the Coriolis-Stokes (CS) force in the wave-averaged momentum and energy equations and make a short analysis of possible energy input to the ocean circulation (i.e., Eulerian mean velocity) from the CS force. Essentially, we find that the CS force appears naturally when considering vertically integrated quantities and that the CS force will not provide any energy input into the system for this case. However, by including the "Hasselmann force", we show some inconsistencies regarding the vertical structure of the CS force in the Eulerian framework and find that there is a distinct vertical structure of the energy input and that the net input strongly depends on whether the wave zone is included in the analysis or not. We therefore question the introduction of the "Hasselmann force" into the system of equations, as the CS force appears naturally in the vertically integrated equations or when Lagrangian vertical coordinates are used.
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