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D K Dey

Publications and source records attributed to D K Dey.

12 recordsLinked to original sources
PubMed2001

Body mass index, weight change and mortality in the elderly. A 15 y longitudinal population study of 70 y olds.

OBJECTIVE: To examine the relationship between body mass index (BMI) at age 70, weight change between age 70 and 75, and 15 y mortality. DESIGN: Cohort study of 70-y-olds. SETTING: Geriatric Medicine Department, Göteborg University, Sweden. SUBJECTS: A total of 2628 (1225 males and 1403 females) 70-y-olds examined in 1971--1981 in Gothenburg, Sweden. RESULTS: The relative risks (RRs) for 15 y mortality were highest in the lowest BMI quintiles of males 1.20 (95% CI 0.96--1.51) and females 1.49 (95% CI 1.14--1.96). In non-smoking males, no significant differences were observed across the quintiles for 5, 10 and 15 y mortality. In non-smoking females, the highest RR (1.58, 95% CI 1.15--2.16) for 15 y mortality was in the lowest quintile. After exclusion of first 5 y death, no excess risks were found in males for following 5 and 10 y mortality across the quintiles. In females, a U-shaped relation was observed after such exclusions. BMI ranges with lowest 15 y mortality were 27--29 and 25--27 kg/m(2) in non-smoking males and females, respectively. A weight loss of > or = 10% between age 70 and 75 meant a significantly higher risk for subsequent 5 and 10 y mortality in both sexes relative to individuals with 'stable' weights. CONCLUSION: Low BMI and weight loss are risk factors for mortality in the elderly and smoking habits did not significantly modify that relationship. The BMI ranges with lowest risks for 15 y mortality are relatively higher in elderly. Exclusion of early deaths from the analysis modified the weight-mortality relationship in elderly males but not in females.

Aged↗
PubMed2001

Height and body weight in elderly adults: a 21-year population study on secular trends and related factors in 70-year-olds.

BACKGROUND: Body size in elderly adults is partly due to aging and partly to secular trends. This study describes secular trends in three anthropometric measures (i.e., height, body weight [BW], and body mass index [BMI]) of 70-year-olds over a period of 21 years and their relation to social and lifestyle factors. METHODS: A total of 3128 70-year-olds from four birth cohorts born between 1901 and 1922 in Gothenburg, Sweden, were examined between 1971 and 1992 in the Geriatric Medicine Department, Göteborg University. Trends in anthropometric measures were examined by permutation test. Influence of the subjects' birth year, physical activity, smoking habits, and education on anthropometric measures were investigated by multiple linear regression. RESULTS: Individuals in later-born cohorts were found to be 1 to 2 cm taller and 1.5 to 6.3 kg heavier than earlier-born cohorts. For BMI, a positive trend was significant only in 70-year-old male participants. "Year of birth" was a positive predictor for BW (p <.001) and BMI (p <.001) in male participants and for height (p <.05) and BW (p <.01) in female participants. Physical inactivity was a positive (p <.01) and "current smoking" a negative (p <.001) predictor for BMI in both sexes. "More than basic education" was a positive predictor for height (p <.001) in both sexes and a negative predictor for body weight (p <.01) and BMI (p <.001) in female participants only. CONCLUSIONS: Trends of increasing height, BW, and BMI were found among the Swedish elderly participants. This may be partly due to differences in smoking habits, physical activity, education, food habits, childhood nutrition, and living conditions between the cohorts.

Aged↗
PubMed2000

A comparison of frailty and other models for bivariate survival data.

Multivariate survival data arise when each study subject may experience multiple events or when study subjects are clustered into groups. Statistical analyses of such data need to account for the intra-cluster dependence through appropriate modeling. Frailty models are the most popular for such failure time data. However, there are other approaches which model the dependence structure directly. In this article, we compare the frailty models for bivariate data with the models based on bivariate exponential and Weibull distributions. Bayesian methods provide a convenient paradigm for comparing the two sets of models we consider. Our techniques are illustrated using two examples. One simulated example demonstrates model choice methods developed in this paper and the other example, based on a practical data set of onset of blindness among patients with diabetic Retinopathy, considers Bayesian inference using different models.

Bayes Theorem↗
PubMed1999

Height and body weight in the elderly. I. A 25-year longitudinal study of a population aged 70 to 95 years.

OBJECTIVE: To describe longitudinal changes in height and body weight between the ages of 70 and 95 y. DESIGN: Longitudinal cohort study with representative sample of 70-y-olds. SETTING: Department of Geriatric Medicine, Göteborg University, Sweden. SUBJECTS: 449 males and 524 females, aged 70 y, living in Göteborg were examined in 1971-72 and this study population participated on 11 occasions during a 25-year follow-up. RESULTS: Mean height decreased 4 and 4.9 cm in males and females respectively and the trend was significant between the ages of 70 and 95 y in both sexes. Between 70 and 75 y of age, a significant difference was found between quintiles of body height where in the highest quintile height was lowered by 0.4 and 0. 3 cm/y, in males and females respectively, and in the lowest quintile by 0.1 cm/y in both sexes. Mean body weight decreased 3.2 and 5.1 kg in males and females respectively, from age 70 to 95 y. The trend was significant over 22 and 20 y for males and females, respectively. Between the ages of 70 and 80 y, individuals in highest quintile of body weight decreased at a rate of 0.8 and 0.6 kg/y, three times higher than those in lowest quintile. Due to the decrease in both height and weight over time, body mass index (BMI) was less affected. CONCLUSION: Height, body weight and BMI decreased significantly in both sexes after age 70 y, and there was a gender difference in the trend. The results can be used as reference data for Swedish elderly and might be of importance to the understanding of anthropometry with the ageing process. SPONSORSHIP: See acknowledgements.

Aged↗
PubMed1999

Multivariate survival analysis with positive stable frailties.

In this paper, we describe Bayesian modeling of dependent multivariate survival data using positive stable frailty distributions. A flexible baseline hazard formulation using a piecewise exponential model with a correlated prior process is used. The estimation of the stable law parameter together with the parameters of the (conditional) proportional hazards model is facilitated by a modified Gibbs sampling procedure. The methodology is illustrated on kidney infection data (McGilchrist and Aisbett, 1991).

Algorithms↗
PubMed1997

Grouped random effects models for Bayesian meta-analysis.

Meta-analysis refers to quantitative methods to combine results from independent studies so as to draw overall conclusions. Frequently, results from dissimilar studies are inappropriately combined, resulting in suspect inferential synthesis. We present a straightforward method to identify and address this problem through the development of grouped random effect models for meta-analysis. We examine 15 comparative studies that investigate the efficacy of a new anti-epileptic drug, progabide. The flexibility of this modelling scheme is exemplified by the result that the open studies support the efficacy of progabide while the closed studies support the reverse hypothesis. Bayesian approaches for meta-analysis are preferable because of the small number of studies prevalent in meta-analysis. We specify diffuse proper prior and hyperprior distributions to assure posterior propriety. We investigate sensitivity of the posterior to choice of prior. We use Gibbs sampling and the Metropolis algorithm to generate samples from the relevant posteriors. We analyse posterior summaries and plots of model parameters to suggest solutions to questions of interest.

Algorithms↗
PubMed1997

A Weibull regression model with gamma frailties for multivariate survival data.

Frequently in the analysis of survival data, survival times within the same group are correlated due to unobserved co-variates. One way these co-variates can be included in the model is as frailties. These frailty random block effects generate dependency between the survival times of the individuals which are conditionally independent given the frailty. Using a conditional proportional hazards model, in conjunction with the frailty, a whole new family of models is introduced. By considering a gamma frailty model, often the issue is to find an appropriate model for the baseline hazard function. In this paper a flexible baseline hazard model based on a correlated prior process is proposed and is compared with a standard Weibull model. Several model diagnostics methods are developed and model comparison is made using recently developed Bayesian model selection criteria. The above methodologies are applied to the McGilchrist and Aisbett (1991) kidney infection data and the analysis is performed using Markov Chain Monte Carlo methods.

Bayes Theorem↗
PubMed1986

Mutagenicity of 4-nitrodiphenyl ether and its metabolites.

The mutagenic potential of 4-nitrodiphenyl ether (NDE) an intermediate of herbicides and an anthelmintic drug, and its reduced products (-NO, -NHOH) were investigated in the Ames test. All the three compounds were potent direct-acting base-pair and frameshift mutagens with activity order -NHOH greater than -NO greater than -NO2. The -NHOH compound has been considered to be the penultimate/ultimate mutagen.

Mutagenicity Tests↗
PubMed1985

Structure-mutagenicity relationships within a series of para-alkoxynitrosobenzenes.

The mutagenic potential of para-alkoxynitrosobenzenes (para substituents, -OCH3, -OC2H5, n-OC4H9, n-OC5H11 and n-OC12H25) and p-phenoxynitrosobenzene was investigated in the Ames test. The order of mutagenic activity within a series of p-alkoxynitrosobenzenes was as follows: p-ethoxy greater than p-methoxy greater than p-butoxy (n) greater than p-pentyloxy (n) greater than p-dodecyloxy (n), the last being inactive. A relationship between mutagenic activity and electronic property of different substituents indicated in the alkoxy series, that as the Hammett constant decreased or bulk of the substituent (except methoxy) increased, the activity was found to decrease.

Mutagens↗