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Mixed Model Approach (mixed + model_approach)
Selected AbstractsMultiplicative random regression model for heterogeneous variance adjustment in genetic evaluation for milk yield in SimmentalJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2008M.H. Lidauer Summary A multiplicative random regression (M-RRM) test-day (TD) model was used to analyse daily milk yields from all available parities of German and Austrian Simmental dairy cattle. The method to account for heterogeneous variance (HV) was based on the multiplicative mixed model approach of Meuwissen. The variance model for the heterogeneity parameters included a fixed region × year × month × parity effect and a random herd × test-month effect with a within-herd first-order autocorrelation between test-months. Acceleration of variance model solutions after each multiplicative model cycle enabled fast convergence of adjustment factors and reduced total computing time significantly. Maximum Likelihood estimation of within-strata residual variances was enhanced by inclusion of approximated information on loss in degrees of freedom due to estimation of location parameters. This improved heterogeneity estimates for very small herds. The multiplicative model was compared with a model that assumed homogeneous variance. Re-estimated genetic variances, based on Mendelian sampling deviations, were homogeneous for the M-RRM TD model but heterogeneous for the homogeneous random regression TD model. Accounting for HV had large effect on cow ranking but moderate effect on bull ranking. [source] Age-related change in breeding performance in early life is associated with an increase in competence in the migratory barn swallow Hirundo rusticaJOURNAL OF ANIMAL ECOLOGY, Issue 5 2007JAVIER BALBONTÍN Summary 1We investigated age-related changes in two reproductive traits (laying date and annual fecundity) in barn swallows Hirundo rustica L. using a mixed model approach to di-stinguish among between- and within-individual changes in breeding performance with age. 2We tested predictions of age-related improvements of competence (i.e. constraint hypothesis) and age-related progressive disappearance of poor-quality breeders (i.e. selection hypothesis) to explain age-related increase in breeding performance in early life. 3Reproductive success increased in early life, reaching a plateau at middle age (e.g. at 3 years of age) and decreasing at older age (> 4 years). Age-related changes in breeding success were due mainly to an effect of female age. 4Age of both female and male affected timing of reproduction. Final linear mixed effect models (LME) for laying date included main and quadratic terms for female and male age, suggesting a deterioration in reproductive performance at older age for both males and females. 5We found evidence supporting the constraints hypothesis that increases in competence within individuals, with ageing being the most probable cause of the observed increase in breeding performance with age in early life. Two mechanisms were implicated: (1) advance in male arrival date with age provided middle-aged males with better access to mates. Yearling males arrived later to the breeding grounds and therefore had limited access to high-quality mates. (2) Breeding pairs maintaining bonds for 2 consecutive years (experienced pairs) had higher fecundity than newly formed inexperienced breeding pairs. 6There was no support for the selection hypothesis because breeding performance was not correlated with life span. 7We found a within-individual deterioration in breeding and migratory performance (arrival date) in the oldest age-classes consistent with senescence in these reproductive and migratory traits. [source] Evaluating the power of monitoring plot designs for detecting long-term trends in the numbers of common guillemotsJOURNAL OF APPLIED ECOLOGY, Issue 3 2006MICHELLE SIMS Summary 1In recent years concerns have been raised regarding the status of the common guillemot Uria aalge in the UK. Numbers have declined in several regions, highlighting the need for continued monitoring of this internationally important population. However, the extent to which the current monitoring scheme is capable of detecting declines and options for improving efficiency has received little attention. 2We investigated the power of different monitoring design options for detecting long-term trends in abundance at a colony of guillemots. The ability to detect trends in abundance was reduced by the large temporal and spatial variability in colony attendance. Taking a linear mixed model approach, we obtained details on the sources and sizes of the variance components using count data collected from monitoring plots on the Isle of May, Scotland, and assessed how best to allocate sampling effort in the light of the count variability structure. 3Our results indicated that trend detection will be improved by counting birds in more plots rather than by increasing the number of counts at existing plots. 4The revisit pattern of counts at the monitoring plots during the seasonal counting period had little effect on trend detection power. However, given the practical issues associated with counting guillemots, alternative revisit patterns to the current approach are preferred. 5For a fixed number of visits per plot, power is strongly influenced by the choice of revisit design if the day-to-day variation in colony attendance is increased. 6Synthesis and applications. Aspects of the UK seabird monitoring scheme can be improved. Changes to the allocation of sampling effort and the plot-revisit pattern will improve both the statistical power to detect long-term trends and the efficiency of conducting the survey. We stress the importance of considering the structure and magnitude of the count variation in a power analysis because judicious design decisions depend on the relative magnitude of these variance components. [source] Assessing fear of falling: Can a short version of the Activities-specific Balance Confidence scale be useful?MOVEMENT DISORDERS, Issue 12 2006Chava Peretz PhD Abstract We present the process of further validation of the 16-item Activities-specific Balance Confidence scale (ABC-16) and a short version (ABC-6) derived by us, to assess balance confidence and fear of falling (FOF). The ABC-16 was administrated to three groups who were anticipated to have a range of balance confidence: 70 patients with higher level gait disorders (HLGDs), 68 healthy controls, and 19 patients with Parkinson's disease (PD). Item reduction was based on identifying items with the lowest scores (high FOF) among the patients. Internal consistency and discriminative validity were assessed using Cronbach's alpha and logistic regression, respectively. The intraclass correlation (ICC) between the short and long versions was assessed using a mixed model approach, accounting for the difference between the scores of the two versions. Six items were found to reflect the most frightening conditions, especially in the patient groups, and to form the short version (ABC-6). Internal consistency of the ABC-16 and ABC-6 were high in the three groups: Cronbach's alpha was between 0.83 and 0.91 and 0.81 and 0.90, respectively. Compared to the control group, the sensitivity of the ABC-16 was 96% for identification of patients with HLGDs (greatest FOF) and 58% for identification of PDs (moderate FOF), based only on the ABC scores. Similar values were obtained for the short version, i.e., 91% for HLGDs and 53% for PDs. ICCs between the short and the long versions was 0.88 (HLGDs), 0.83 (PDs), and 0.78 (Controls). To conclude, the short version of the ABC has properties analogous to the parent questionnaire and is apparently useful in assessing FOF. © 2006 Movement Disorder Society [source] Urban-Rural Differences in Motivation to Control Prejudice Toward People With HIV/AIDS: The Impact of Perceived Identifiability in the CommunityTHE JOURNAL OF RURAL HEALTH, Issue 3 2008Janice Yanushka Bunn PhD ABSTRACT:,Context:HIV/AIDS is occurring with increasing frequency in rural areas of the United States, and people living with HIV/AIDS in rural communities report higher levels of perceived stigma than their more urban counterparts. The extent to which stigmatized individuals perceive stigma could be influenced, in part, by prevailing community attitudes. Differences between rural and more metropolitan community members' attitudes toward people with HIV/AIDS, however, have rarely been examined. Purpose: This study investigated motivation to control prejudice toward people with HIV/AIDS among non-infected residents of metropolitan, micropolitan, and rural areas of rural New England. Methods: A total of 2,444 individuals were identified through a random digit dialing sampling scheme, and completed a telephone interview to determine attitudes and concerns about a variety of health issues. Internal or external motivation to control prejudice was examined using a general linear mixed model approach, with independent variables including age, gender, community size, and perceived indentifiability within one's community. Findings: Results showed that community size, by itself, was not related to motivation to control prejudice. However, there was a significant interaction between community size and community residents' perceptions about the extent to which people in their communities know who they are. Conclusion: Our results indicate that residents of rural areas, in general, may not show a higher level of bias toward people with HIV/AIDS. The interaction between community size and perceived identifiability, however, suggests that motivation to control prejudice, and potentially the subsequent expression of that prejudice, is more complex than originally thought. [source] | |||||||||||||