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D Commenges

Publications and source records attributed to D Commenges.

At least 37 records · Page 2Linked to original sources
PubMed1995

Development of the WPC approach and application to linkage analysis of breast cancer.

We develop the weighted pairwise correlation approach in several directions: we use a method based on martingale residuals rather than rank residuals; we give a measure of the strength of the linkage and we propose a method for multipoint analysis by combining the weights used in the statistics for different markers. These tools are applied to 214 breast cancer families. The values of the test statistics for the different markers are very similar to those obtained with the lod-score approach; the multipoint analysis increases the value of the test statistic and is also in agreement with previous results.

Breast Neoplasms↗
PubMed1995

Score test of homogeneity for survival data.

If follow-up is made for subjects which are grouped into units, such as familial or spatial units then it may be interesting to test whether the groups are homogeneous (or independent for given explanatory variables). The effect of the groups is modelled as random and we consider a frailty proportional hazards model which allows to adjust for explanatory variables. We derive the score test of homogeneity from the marginal partial likelihood and it turns out to be the sum of a pairwise correlation term of martingale residuals and an overdispersion term. In the particular case where the sizes of the groups are equal to one, this statistic can be used for testing overdispersion. The asymptotic variance of this statistic is derived using counting process arguments. An extension to the case of several strata is given. The resulting test is computationally simple; its use is illustrated using both stimulated and real data. In addition a decomposition of the score statistic is proposed as a sum of a pairwise correlation term and an overdispersion term. The pairwise correlation term can be used for constructing a statistic more robust to departure from the proportional hazard model, and the overdispersion term for constructing a test of fit of the proportional hazard model.

Graft Rejection↗
PubMed1995

Visuo-spatial attention and psychomotor performance in elderly community residents: effects of age, gender, and education.

In cross-sectional analysis of 1,799 subjects of the Paquid Research Program, an epidemiological study on brain aging conducted in the Bordeaux area (France), we have studied the effects of age, gender, and education level on psychometric tests requiring visuo-spatial focused attention and psychomotor performance. Although previous studies suggest that normal aging produces no significant change in focused attention, we did observe lower attentional abilities and lower speed of execution with increasing age. Female gender and low education level were also related to poorer attention and psychomotor performance. As the effects of these individual factors are difficult to disentangle from each other on the small samples of subjects used in group studies, epidemiological surveys seem useful to provide a better understanding of the neuropsychology of aging.

Age Factors↗
PubMed1995

Social and leisure activities and risk of dementia: a prospective longitudinal study.

OBJECTIVE: To study the relationship between social and leisure activities and risk of subsequent dementia in older community residents. SETTING: A cohort study of people aged 65 and older were followed-up 1 and 3 years after a baseline screening (the Paquid study). PARTICIPANTS: 2040 older subjects living at home in Gironde (France) were randomly selected and followed for at least 3 years. DATA COLLECTION: Information about social and leisure activities was collected during the baseline screening with an interview by a psychologist. Incident cases of dementia were detected during the first and third year follow-up screenings according to the DSM-III-R criteria. MAIN RESULTS: All but one of the social and leisure activities noted were significantly associated with a lower risk of dementia. Only golden club participation was not significantly associated with this risk. After adjustment for age and cognitive performance measured by the Mini-Mental State Exam, visual memory test, and verbal fluency test, only traveling (Relative risk (RR) = .48,95% Confidence Interval (95% CI) = .24-.94), odd jobs or knitting (RR = .46,95% CI = .26-.85), and gardening (RR = .53, 95% CI = .28-.99) remained significant. CONCLUSIONS: Regular participation in social or leisure activities such as traveling, odd jobs, knitting, or gardening were associated with a lower risk of subsequent dementia.

Aged↗
PubMed1995

Score test for familial aggregation in probands studies: application to Alzheimer's disease.

When studying familial aggregation of a disease, the following two-stage design is often used: first select index subjects (cases and controls); then record data on their relatives. The likelihood corresponding to this design is derived and a score test of homogeneity is proposed for testing the hypothesis of no-aggregation. This test takes into account the selection procedure and allows adjustment to be made for explanatory variables. It appears as the sum of three terms: a pure test of homogeneity, a test of comparison of observed minus expected cases in the two groups, and a term which adjusts for the possible unequal probabilities of disease of the index subjects. Asymptotic efficiency and a simulation study show that the proposed test is superior to either the pure homogeneity test or tests based on the comparison of numbers of affected in the two groups. The test statistic, which has an asymptotically standard normal distribution, is applied to a study of familial aggregation of early-onset Alzheimer's disease for which a highly significant value (9.46) is obtained: this is the highest value among the three tests compared, in agreement with the simulation study. A logistic normal model is fitted to the data, taking account of the selection procedure: it allows to estimate the regression parameters and the variance of the random effect; the likelihood ratio test for familial aggregation seems less powerful than the score test.

Alzheimer Disease↗
PubMed1994

Components of drinking water and risk of cognitive impairment in the elderly.

The relation between aluminum, fluorine, calcium, and pH in drinking water and the risk for cognitive impairment was studied using data collected in 1988-1989 in a population-based survey of 3,777 French men and women aged 65 years and older (the Paquid study). Cognitive impairment was defined as a score lower than 24 on the Mini-Mental State Examination. Data related to drinking water came from two prospective measurement surveys whose reliability was checked by a variability study. A mixed effects logistic regression was performed, adjusting for the effects of the age, sex, educational level, and occupation of the participants. A significant protective effect was found for high calcium concentration (odds ratio = 0.8 for a concentration > or = 75 mg vs. < 75 mg, p = 0.015). For aluminum, no significant effect was found when pH was not included in the model, but the results showed a weak interaction between aluminum and pH. When the four variables (calcium, aluminum, pH, and aluminum x pH interaction) were considered in the statistical analysis as a group, this group was significantly related to cognitive impairment (p = 0.01).

Aged↗
PubMed1994

Robust genetic linkage analysis based on a score test of homogeneity: the weighted pairwise correlation statistic.

In testing genetic linkage using large or complex pedigrees, robust methods may be preferred to the Lod-score method. The affected-pedigree-member method is robust but does not use the information available in nonaffected subjects, which results in a loss of power. We propose a new test of genetic linkage based on a score test of homogeneity derived from a random effect model. The statistic is simple and uses only pairs of subjects. In contrast with the affected-pedigree-method, it uses all the available pairs and does not depend on the marker alleles frequencies. A rank version of this weighted pairwise correlation statistic is proposed, its exact first and second moment derived. We show that for age-dependent diseases, it provides a simple nonparametric test.

Age of Onset↗
PubMed1994

The weighted rank pairwise correlation statistic for linkage analysis: simulation study and application to Alzheimer's disease.

The weighted rank pairwise correlation (WRPC) statistic has been proposed as a robust test of genetic linkage, particularly adapted to the analysis of large and complex pedigrees and for age-dependent and heterogeneous diseases. In this paper a simulation study is presented. Validity and power of the WRPC test are studied and compared to the Haseman-Elston sibpair method for various types of problems. The power of the WRPC test is slightly lower than the Haseman-Elston method for analyzing a large number of small randomly chosen pedigrees. It is higher however in presence of genetic heterogeneity or for analyzing large individual pedigrees. Recently, evidence of linkage of Alzheimer's disease with a locus on chromosome 14, D14s43, has been obtained by the Lod-score method. We reanalyze these data using the WRPC test, essentially confirming the results of the Lod-score method. The WRPC test statistic is higher than the equivalent Lod-score statistic for the two pedigrees which show strong evidence of linkage with the two methods. The global WRPC test statistic is slightly lower than the Lod-score test statistic. The WRPC test, however, makes no hypothesis of a specific genetic transmission model and can be computed very quickly; in addition, an exact P-value can be computed by simulation for individual pedigrees.

Alzheimer Disease↗
PubMed1994

Tobacco consumption and cognitive impairment in elderly people. A population-based study.

We examined the relationship between tobacco consumption and Alzheimer's disease (AD), cognitive deficit, and memory performances in elderly community residents of southwestern France. Subjects were considered to have a cognitive deficit if they scored under 24 on the French version of the Mini-Mental State Examination, and poor memory performances if they scored under 8 on the Benton Visual Retention Test. Among the 3770 subjects who gave information about their smoking habits, only 356 (9.5%) were current smokers, 998 (26.5%) were past smokers, and 2416 (64%) were never smokers. Current smokers (odds ratio (OR) = 0.52, P < 0.001) and past smokers (OR = 0.54, P < 0.001) had a lower risk of cognitive deficit than did never smokers. However, this significant relationship disappeared after adjustment for potential confounding factors such as occupational category (OR = 0.91 (not significant) for current smokers and OR = 0.87 (not significant) for past smokers). Similar results were obtained for the risk of AD and of poor memory performances. The apparent protective effect of smoking habits on cognitive abilities could be due to a confounding effect of occupational category.

Aged↗
PubMed1994

Incidence of dementia and Alzheimer's disease in elderly community residents of south-western France.

BACKGROUND: Dementia is a growing problem in developed countries. The aim of this paper is to estimate incidence rates of dementia, Alzheimer's disease and vascular dementia in a community population of South-Western France. METHODS: A sample of 2792 subjects was selected and followed-up 1 year and 3 after the initial screening. At each visit, a standardized questionnaire was administered by trained psychologists. Demented subjects were identified using a two-step procedure. The first step consisted of a systematic screening by the psychologist using DSM IIIR criteria for dementia. In the second step, subjects who fulfilled the DSM IIIR criteria were examined by a neurologist. NINCDS-ADRDA criteria were applied to diagnose Alzheimer's disease. RESULTS: Incidences of dementia and Alzheimer's disease were estimated at 16.3 and 11.4 per 1000 per year, respectively. Incidence estimates increased with age from 2 per 1000 in subjects aged 65-69 years to 74 per 1000 in subjects > 90 years. Incidence estimates of Alzheimer's disease showed the same increased from 0.7 per 1000 to 66 per 1000. Incidences of dementia and of Alzheimer's disease did not level off with age and were not different between genders.

Aged↗
PubMed1994

Test of homogeneity of binary data with explanatory variables.

Apparent heterogeneity of the risk of a disease in different groups may be explained by subject-specific risk factors unequally distributed in these groups. We propose a score test of homogeneity that allows adjustment for known risk factors of the disease. The test is based on a random-effect logistic regression model and requires only simple computations in addition to a conventional logistic regression method. The score test is applied to the study of geographical heterogeneity of cognitive impairment in elderly using a sample of 3,318 subjects scattered in 75 parishes. It is shown that an apparent heterogeneity disappears when taking into account subject-specific risk factors. This test may also be useful for studying familial aggregation of a disease.

Epidemiologic Methods↗
PubMed1994

The intraclass correlation coefficient: distribution-free definition and test.

A definition of the intraclass correlation coefficient is given on the basis of a general class of random effect model. The conventional intraclass correlation coefficient and the intracluster correlation coefficient for binary data are both particular cases of the generalized coefficient. We derive the score test for the hypothesis of null intraclass correlation in the exponential family. The statistic does not depend on the particular distribution in this family and is related to the pairwise correlation coefficient. The test can be adjusted for explanatory variables.

Aged↗
PubMed1993

An empirical Bayes approach to the estimation of the incidence curve of HIV infection.

A new approach is proposed for estimating the incidence curve of HIV infection and obtaining short term prediction of AIDS incidence. It is based on the method of back calculation which utilizes the fact that AIDS incidence is generated from HIV infection incidence by convolution with the incubation period distribution, but avoids the difficulties associated with approximating the infection incidence curve by a class of step functions. Instead, the infection incidence is modelled as a simple stochastic epidemic process which ensures smoothness of the estimate. We first derive the distribution of AIDS incidence knowing infection incidence. The best linear estimators of infection incidence as well as future AIDS incidence are given; a smoothed past AIDS incidence is also obtained. The parameters of the stochastic infection process can be estimated by maximum likelihood using a normal approximation to the marginal distribution of the AIDS incidence. This approach is applied to AIDS incidence data in the United States up to mid 1987. We find that the epidemic started in mid 1976, peaked at the end of 1983 and dropped afterwards.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Linkage analysis of Alzheimer's disease with methods using relative pairs.

Four relative-pair methods for detecting genetic linkage were applied to familial Alzheimer's disease data. Results obtained using an extended Haseman-Elston test and a weighted rank pairwise correlation test, which both use information from all relative pairs, were consistent with previously published likelihood results and appear to be more powerful than affected sib pair methods.

Alzheimer Disease↗
PubMed1993

Cerebral and functional aging: first results on prevalence and incidence of the Paquid cohort.

Paquid is an interdisciplinary study designed to investigate cerebral and functional aging. A cohort of 3,777 community residents living in two administrative areas of South-Western France was selected. A standardized questionnaire was administered at home by trained psychologists. The same procedure was applied one and three years after the baseline data collection. The identification of demented subjects was made with a two-step procedure. The first step is a systematic screening by the psychologists using the DSM-III criteria for dementia. Subjects who fulfilled the DSM-III criteria were examined by a neurologist. Diagnosis of dementia is confirmed according to the NINCDS-ADRDA criteria. The Paquid cohort is complemented by a random sample of 357 institutionalized subjects. First results of prevalence and incidence rates show an exponential increase of dementia with age.

Aged↗
PubMed1993

[Prevalence of dementia in Gironde (France)].

The objective of the study is to estimate the prevalence of dementia using the data of the Paquid cohort. A sample of 3,149 subjects aged 65 years and older living at home or in institution was randomly chosen in Gironde (France). A questionnaire and psychometric tests were used to evaluate cognitive functioning and the presence of dementia was assessed through DSM III Diagnostic and Statistical Manual of mental disorders (ed. III) criteria. Hachinski scale and work group NINCDS-ADRDA criteria were applied to confirm the presence of dementia and identify Alzheimer's disease. Overall prevalence was estimated to 4.3%. No difference was found between men and women. The prevalence increased with age with nearly a doubling every 5 years of age. In institution, dementia frequency remained stable. The relative risk of a demented subject to be institutionalized with regard to a non demented subject decreased with age.

Aged↗
PubMed1992

Comparison of the proportions of affected relatives of cases and controls: analysis and minimum sample size formula.

The problem of familial aggregation has frequently been approached by comparing the proportion of affected relatives of index cases with the proportion of affected relatives of index controls. This type of study has an analogy with the case-control design and is frequently analysed as if it was one. It is however an essentially different design which may involve dependent observations. We show that conventional tests for comparing proportions of affected subjects are still valid with this design; we give a formula for computing the minimum sample size required to detect a given degree of aggregation measured by the intracluster correlation coefficient, which can be estimated very simply by the difference in proportions of affected relatives in the two groups.

Case-Control Studies↗