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International Journal of Statistics in Medical Research

A Contribution to the Genetic Epidemiology of Structured Populations
Pages 277-281
Alan E. Stark
DOI:
http://dx.doi.org/10.6000/1929-6029.2015.04.03.5
Published: 19 August 2015


Abstract: A matingsystem, previously derived, which is more general than random mating is defined by the gene frequency q and a parameter F which measures divergence from Hardy-Weinberg proportions commonly used in genetic analysis. F can be viewed as the average coefficient of inbreeding in a population, the use emphasized here. Also it can characterize the variation in gene frequency in a stratified population. Taking q as fixed, the distribution of F over values admissible under the general mating system is derived by simulation. The mating system may be seen to be based on indifference as to choice of mates. This is the first object of the paper. The second uses the derived distribution of F to make a Bayesian estimate of F from a single sample of genotypic counts. Such an estimate has a number of uses in genetic analysis.

Keywords: Genetic Equilibrium, Hardy-Weinberg Law, Mate choice indifference, Inbreeding coefficient, Bayesian estimation.
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Survival Analysis of Duration of Breastfeeding and Associated Factors of Early Cessation of Breastfeeding in Ethiopia
Pages 71-79
Melkamu Molla and Leakemariam Berhe
DOI:
http://dx.doi.org/10.6000/1929-6029.2016.05.02.1
Published: 02 June 2015


Abstract: The purpose of this study was to assess the duration of breastfeeding among women of reproductive age in Ethiopia and to identify determinants associated with early cessation of breastfeeding. Data for the study were drawn from the Ethiopia Demographic and Health Survey 2005. The study included mothers of 9,066 children from nine regional states and two city administrations. The Kaplan-Meier and stratified Cox’s hazard model were employed for the analysis of breastfeeding-related data. The Kaplan-Meier survival estimate showed that the probability of mothers who continue to breastfeeding was high (97.3%) for the first month. The breastfeeding rates then declined to 92.5% at 6 months, 78.4% at 12 months, 37% at 24 months and 8.3% at 48 months. The mean and median duration of breastfeeding in Ethiopia were 25.64 and 24.00 months respectively. The stratified Cox regression analysis revealed that younger mothers, mothers who had lived in urban area, mothers having higher education, higher maternal parity, early pregnant and being a Muslim and protestant were significant determinants of early cessation of breastfeeding in Ethiopia. Then, we recommend that the breastfeeding-promotion programs in Ethiopia should give special attention to young mothers, those who lived in urban areas, mothers with higher education, those who have higher parity, those who have early pregnancy and who are Muslims and Protestants since these mothers tend to breastfeed their child for a relatively shorter period of time.

Keywords: Breastfeeding duration, Kaplan-Meier estimator, Determinants, Stratified- Cox regression model, Hazard-Ratio, Ethiopia.
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A Natural Experiment for Inferring Causal Association between Smoking and Tooth Loss: A Study of a Workplace Contemporary Cohort
Pages 331-336
Takashi Hanioka, Satoru Haresaku, Nao Suzuki, Kaoru Shimada, Takeshi Watanabe, Miki Ojima, Keiko Fujiie and Masako Watanabe
DOI:
http://dx.doi.org/10.6000/1929-6029.2015.04.04.3
Published: 03 November 2015


Abstract: Background: Natural experiments in former smokers are an important criterion for inferring causality between smoking and tooth loss. We examined how former smoking influenced risk estimate of tooth loss incidence.

Methods: Records of dental check-ups of the work cohort were examined. The sample consisted of data from 1,724 workers recorded at the ages of 40 years and 50 years, and this was analyzed for tooth loss incidence during a 10-year period. Former smokers were categorized into two groups based on whether they quit smoking before or during the observational period. Variables used for adjustment were age, sex, oral and overall health behavior, dental visit, and number of existing teeth immediately prior to observation.

Results: The prevalence of tooth loss incidence and number of teeth lost during the observational period were both higher in current smokers than in never smokers (33.7% vs. 23.9% and 0.83 vs. 0.42, respectively). Incident odds ratio of tooth loss in long-term quitters relative to never smokers was not significant and less than one (incident odds ratio 0.85, 95% confidence interval 0.56–1.29). Incident odds ratios of short-term quitters and current smokers were both significant, though short-term quitters exhibited higher values (1.72, 1.15–2.55) than current smokers (1.48, 1.10–2.00).

Conclusions: The causal interpretation is strengthened by attenuation of the risk in long-term quitters. However, additional factors may influence the risk estimates of former smokers, suggesting potential limitations of a natural experiment for inferring causal association between smoking and tooth loss.

 

Keywords: Natural experiment, Smoking, Tooth loss, Cohort study, Causal inference.
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International Journal of Statistics in Medical Research

A Contribution to the Genetic Epidemiology of Structured Populations
Pages 277-281
Alan E. Stark
DOI:
http://dx.doi.org/10.6000/1929-6029.2015.04.03.5
Published: 19 August 2015


Abstract: A matingsystem, previously derived, which is more general than random mating is defined by the gene frequency q and a parameter F which measures divergence from Hardy-Weinberg proportions commonly used in genetic analysis. F can be viewed as the average coefficient of inbreeding in a population, the use emphasized here. Also it can characterize the variation in gene frequency in a stratified population. Taking q as fixed, the distribution of F over values admissible under the general mating system is derived by simulation. The mating system may be seen to be based on indifference as to choice of mates. This is the first object of the paper. The second uses the derived distribution of F to make a Bayesian estimate of F from a single sample of genotypic counts. Such an estimate has a number of uses in genetic analysis.

Keywords: Genetic Equilibrium, Hardy-Weinberg Law, Mate choice indifference, Inbreeding coefficient, Bayesian estimation.
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International Journal of Statistics in Medical Research

Age Scale for Assessing Activities of Daily Living
Pages 48-56
Rafael Figueroa, Satoshi Seino, Noriko Yabushita, Yoshiro Okubo, Yosuke Osuka, Miyuki Nemoto, Songee Jung and Kiyoji Tanaka
DOI:
http://dx.doi.org/10.6000/1929-6029.2015.04.01.5
Published: 27 January 2015


Abstract: The purpose of this study was to develop an age scale for assessing activities of daily living (ADL) among community-dwelling adults aged 75 years or older. Participants were 1006 older Japanese: 312 men (79.6 ± 4.3 years) and 694 women, (79.9 ± 5.5 years). Participants completed a battery of 8 performance tests related to ADL and the Barthel index (BI) questionnaire. Spearman rank-order correlation analysis was applied to obtain the correlation of the 8 ADL performance tests with the total BI score. Three variables were high rank-order correlated with BI, secondly those items were subjected to the principal component analysis. The weighted combination of the principal component scores was summed. Resulting in an ADL score (ADLS), women = 0.075 X1 – 0.082 X2 – 0.063 X3 + 0.124, men = 0.051 X1 – 0.105 X2 – 0.099 X3 + 0.249, where X1 = hand-grip strength, X2 = timed up and go, X3 = five-chair sit to stand. Individual ADLS was transformed to an ADL age scale (ADLA). The estimation was – 5.493 ADLS + 79.90 for women, and – 4.272 ADLS + 79.57 for men. Due to the distortion at the regression edges, the equation was corrected as suggested by Dubina et al. ADLA women after correction was = 0.447 (chronological age: CA) – 5.49ADLS + 44.17, men = 0.519CA – 4.27ADLS + 38.26. ADLA can be used to identify or monitor the characteristics of the ADL levels of physical abilities in older Japanese aged 75 years or older.

Keywords: Age assessment, principal component analysis, physical function, 75 years and older, older Japanese.
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