| 1. |
- 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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| 7. |
- 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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| 8. |
- 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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| 10. |
- 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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| 11. |
- 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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| 12. |
- Broström, Göran, et al.
(författare)
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Partial Partial Likelihood
- 2008
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Ingår i: Communications in statistics. Simulation and computation. - : Taylor & Francis. - 0361-0918 .- 1532-4141. ; 37:4, s. 679-686
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Tidskriftsartikel (refereegranskat)abstract
- The maximum likelihood and maximum partial likelihood approaches to the proportional hazards model are unified. The purpose is to give a general approach to the analysis of the proportional hazards model, whether the baseline distribution is absolutely continuous, discrete, or a mixture. The advantage is that heavily tied data will be analyzed with a discrete time model, while data with no ties is analyzed with ordinary Cox regression. Data sets in between are treated by a compromise between the discrete time model and Efron's approach to tied data in survival analysis, and the transitions between modes are automatic. A simulation study is conducted comparing the proposed approach to standard methods of handling ties. A recent suggestion, that revives Breslow's approach to tied data, is finally discussed.
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| 13. |
- Corell, Hanna, 1977-, et al.
(författare)
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Wind sensitivity of the inter-ocean heat exchange
- 2009
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Ingår i: Tellus. Series A, Dynamic meteorology and oceanography. - : Stockholm University Press. - 0280-6495 .- 1600-0870. ; 61:5, s. 635-653
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Tidskriftsartikel (refereegranskat)abstract
- An idealised two-basin model is used to investigate the impact of the wind field on the heat exchange between the ocean basins. The scalar potential of the divergent component of the horizontal heat flux is computed, which gives a 'coarse-grained' image of the surface heat flux that captures the large-scale structure of the horizontal heat transport. Further the non-divergent component is examined, as well as the meridional heat transport and the temperature–latitude overturning stream function. A sensitivity analysis examines the heat transport response to changes in wind stress at different latitudes. The results are compared with results from an eddy-permitting global circulation model. The westerly wind stress over the Southern Ocean has two effects: a local reduction of the surface heat loss in response to the equatorward surface Ekman drift, and a global re-routing of the heat export from the Indo-Pacific. Without wind forcing, the Indo-Pacific heat export is released to the atmosphere in the Southern Ocean, and the net heat transport in the southern Atlantic is southward. With wind forcing, the Indo-Pacific export enters the Atlantic through the Aghulas and is released in the Northern Hemisphere. The easterlies enhance the poleward heat transport in both basins.
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| 15. |
- Karlsson, Maria, 1975-
(författare)
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Estimators of semiparametric truncated and censored regression models
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contributes in several ways to the existing knowledge on estimation of truncated, censored, and left truncated right censored (LTRC) regression models. Three new semiparametric estimators are proposed, allowing for asymmetric error distributions. A bootstrap method for estimation of the covariance matrix of the quadratic mode estimator (QME) is proposed and studied. In addition, finite sample properties of estimators for truncated, censored, and LTRC data are studied within simulation studies and applications with real data. The first paper consists of a simulation study of the QME and other estimators of truncated regression models. The paper contributes with results suggesting the bootstrap technique being potentially useful for estimation of the QME covariance matrix. In the second paper estimators of truncated and censored semiparametric regression models are proposed. These estimators are generalizations of the QME and the winsorized mean estimator (WME) by allowing asymmetric ``trimming'' of observations. Consistency and asymptotic normality of the estimators are shown. By combining the two moment restrictions used to derive the estimators in the second paper, a consistent estimator of LTRC regression models is proposed in the third paper. The fourth paper contains an application where LTRC interpurchase intervals of cars are analysed. Results regarding the interpurchase behaviour of consumers are provided, as are results on estimator properties.
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| 17. |
- Lindkvist, Marie, et al.
(författare)
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Interaction between fertility and infant mortality in an intergenerational perspective
- 2008
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Ingår i: ESSHC Conference in Lisbon, 26 February-1 March, 2008.
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Konferensbidrag (refereegranskat)abstract
- Many studies in the past have emphasized the positive correlation between infant mortality and fertility, but how this operates remain unclear. In this paper, we investigate these interdependent processes using data from the Demographic Data base at Ume{\aa} University. More specifically, we have data from regions in the northern part of Sweden, starting in the fifteenth century and ending around the year 1900. In an earlier paper, we have studied the intergenerational aspects of infant mortality and in this paper we incorporate fertility. We investigate the interaction between the two processes and how patterns are tranferred from generation to generation.
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| 21. |
- Nycander, Jonas, et al.
(författare)
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Thermodynamic analysis of ocean circulation
- 2007
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Ingår i: Journal of Physical Oceanography. ; 37, s. 2038-2052
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Tidskriftsartikel (refereegranskat)abstract
- Calculating a stream function as function of depth and density is proposed as a new way of analysing the thermodynamic character of the overturning circulation in the global ocean. The sign of an overturning cell in this stream function directly shows whether it is driven mechanically by large-scale wind stress, or ''thermally'' by heat conduction and small scale mixing. It is also shown that the integral of this stream function gives the thermodynamic work performed by the fluid. The analysis is also valid for the Boussinesq equations, although formally there is no thermodynamic work in an incompressible fluid. The proposed method is applied both to an idealized coarse-resolution three-dimensional numerical ocean model, and to the realistic high-resolution OCCAM model. It is shown that the overturning circulation in OCCAM between 200 m and 1000 m depth is dominated by a thermally indirect cell of 24 Sv, forced by Ekman pumping. In the densenst and deepest waters there is a thermally direct cell of 18 Sv, which requires a forcing by around 100 GW of parameterized small-scale mixing.
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| 22. |
- Omnell-Persson, Marie, et al.
(författare)
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Living donors - How far can we proceed? A brief report on a Swedish interview study
- 2008
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Ingår i: Organ Transplantation: Ethical, Legal and Psychosocial Aspects - Towards a Common European Policy. - 9783899674156 ; , s. 270-274
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Konferensbidrag (refereegranskat)abstract
- In Sweden "anonymous living donation'' (ALD) has recently been performed but is still under evaluation. We considered it important to learn more about the thoughts of the volunteers for such a donation. Five persons out of ten people who had volunteered to donate anonymously at the transplant unit at Malmo University Hospital were interviewed. The main reason for the wish to donate was the possibility to help another person. One informant thought it was logical and the one who had donated said he wanted to make someone really happy. When asked about possible consequences of the donation the spontaneous answers were related to medical risks and none mentioned psychological risks. The informants in this study, although only five, did not tell us anything that, in our opinion, would contradict ALD but these interviews highlight some points of view regarding anonymous living donation that deserve further discussion.
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