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D Hémon

Publications and source records attributed to D Hémon.

At least 55 records · Page 3Linked to original sources
PubMed1993

Comparison of three methods of estimating odds ratios from a job exposure matrix in occupational case-control studies.

A job exposure matrix consists of jobs on one axis and substances on the other, with the matrix elements describing the likelihood of an individual's exposure to a substance in a given job. This can be used in case-control studies to infer exposures of subjects whose jobs are known. The simplest form of job exposure matrix contains binary entries, but it is also possible to envisage continuous variables describing the probability of exposure in the job (probabilistic matrix). In such a case, the user has various options for transforming and analyzing the data, including the following: 1) transform to binary variables and analyze as conventional binary exposure variables; 2) leave as continuous variables and analyze using logistic regression; 3) leave as continuous variables and analyze using a linear model. Simulations were carried out to compare the ability of the three methods to estimate odds ratios under 36 experimental conditions. The linear model produced unbiased estimates, the logistic model produced somewhat biased estimates at high odds ratios, and the transformation to a binary variable produced systematically low estimates in most experimental circumstances. With the linear and logistic models, the odds ratio estimators had similar precision when the bias of the latter was not too great. The authors conclude that the linear model permits optimal use of a probabilistic matrix in an epidemiologic study and hope that these results will encourage the development of job exposure matrices containing probabilities rather than dichotomies.

Case-Control Studies↗
PubMed1993

Retrospective evaluation of the exposure to polycyclic aromatic hydrocarbons: comparative assessments with a job exposure matrix and by experts in industrial hygiene.

This work aimed at assessing the validity of job exposure matrix (JEM) for the retrospective evaluation of exposure to polycyclic aromatic hydrocarbons (PAH) within the framework of population-based case-control studies, taking the evaluation of industrial hygiene experts as reference. For this purpose, we used a case-control study for which the different levels of exposure were assessed by such experts after case by case evaluation of all job periods reported by the subjects. The JEM was applied to this set of data so that we had, according to job periods, the experts' evaluation on the one hand, and the JEM evaluation on the other. JEM sensitivity and specificity of the matrix vary widely from 0.13 to 0.96 and 0.58 to 0.99 respectively, depending on whether the experts chose a narrow or wide definition of exposure and on the cutoff point chosen to dichotomize the JEM. We also computed, according to the sensitivity and specificity of the JEM, the odds ratio (OR) and relative efficiency (RE) given by the JEM for several hypothetical OR and frequencies of exposure among the controls. These calculations were made for different definitions of exposure by the experts and different cutoff points for the JEM. The results show a bias in the JEM's evaluation of the OR. In addition, the RE varies widely from very low values to high values (0.05-0.45) depending on the experts' definition of exposure and the cutoff point chosen for the matrix. Note, however, that all these calculations were made taking the experts' evaluation as the reference.(ABSTRACT TRUNCATED AT 250 WORDS)

Case-Control Studies↗
PubMed1993

Standardization in the retrospective evaluation by experts of occupational exposure to organic solvents in a population-based case-control study.

Epidemiologists carrying out retrospective evaluation of occupational exposure to solvents often use experts to assist in drawing up and interpreting structured questionnaires. However the epidemiologist cannot pass complete responsibility to the expert for deciding on the relative importance of the different exposure variables. Expert assessment of exposure to organic solvents was carried out in a population-based case-control study. The process of expert evaluation was examined and the different steps in the process identified. This paper describes work in progress on the formalization of the rules that experts use to identify and quantify exposure.

Case-Control Studies↗
PubMed1993

Retrospective evaluation of occupational exposures in population-based case-control studies: general overview with special attention to job exposure matrices.

Different approaches may be considered in the evaluation of past occupational exposures: questionnaires only, questionnaires and experts (such as industrial hygienists or occupational physicians), questionnaires and job exposure matrices (JEM). These approaches are described in this paper and their use in the framework of population-based case-control studies is discussed. The use of experts to assess exposure from questionnaires is generally considered to be the reference method. Its major drawbacks are its cost and the shortage of experienced experts. On the other hand, JEM reduce the cost of the study and provide an objective way of evaluating exposures. The main drawback of JEM is the fact that they can produce misclassification. The development of a JEM includes the choice of the job classification system which influences the degree to which the matrix can be used in other studies, the precise definition of exposures, and the choice of entries which provide more information than the oversimplified exposed/non-exposed dichotomy. Recent results on JEM methodology (statistical methods of analysis and evaluation of JEM quality) should encourage both their development and their use in epidemiological studies.

Case-Control Studies↗
PubMed1993

Studying the performance of a job exposure matrix.

During the last decade, the use of job exposure matrices (JEM) in occupational studies has grown but uncertainty remains among epidemiologists and industrial hygienists regarding this methodology and appropriate methodological tools are needed to study the performance of JEM. It must first be emphasized that a true validation can rarely be achieved and that the performance of a JEM must be tested against the exposure evaluation of another method taken as a reference, such as expert assessment. This comparison comprises three main elements: the ability of the JEM to evaluate accurately the exposure itself, its statistical performances in terms of bias and power and its ability to detect known associations between risk factors and disease. When comparing JEM and experts, all aspects of the two methods have to be looked at and a balance struck between the advantages and shortcomings of each of them. The problem should not be reduced to a trade-off between the precision provided by experts and the cost savings possible by using JEM. Finally, it is important to avoid a systematic opposition between JEM and expert assessments, as one positive result of their comparison may be the improvement of both methods of exposure evaluation.

Bias↗
PubMed1993

Retrospective evaluation of occupational exposure to organic solvents: questionnaire and job exposure matrix.

Correct retrospective assignment of subjects to an exposure category is affected by a variety of problems: 1) lack of an objective lifetime measurement; 2) dependence upon the accuracy and thoroughness of the job description; 3) heavy reliance upon the knowledge of experts. The aim of the study was the quantification of the performance of a job exposure matrix (JEM) in evaluating solvent exposure, using expert judgements as the reference method. The sources of discrepancies between the two methods were analysed within the framework of two community-based case-control surveys. One included 765 cases of bladder cancer (BC) and 765 controls, the other 298 cases of glomerulonephritis (GN) and 298 controls. The JEM had been set up previously for a case-control study on laryngeal cancer and is based on 4000 discrete job titles. Comparison between the JEM and expert exposure evaluation was carried out for 2736 job periods in the BC study and 929 in the GN study. Categories of exposure for both experts and JEM were dichotomized, using different cutoff points for exposure and non-exposure. Prevalence of exposure as assessed by the experts was twice as high in the GN study (19%) as in the BC study (10%), showing the importance of the questionnaire design and of the inclusiveness of the definition of exposure. Sensitivity of the JEM vis-a-vis the experts was low (23-63%), whereas specificity was rather high (87-98%). The best concordance between the two methods was obtained with a specific dichotomy from the JEM and a narrow definition of exposure by the experts. Bias and loss of power resulting from JEM misclassifications were calculated with a theoretical population odds ratio of 3 and an exposure prevalence of 10%. If the experts' classification of the subjects according to exposure is assumed to be 100% correct, using the JEM led to a bias in estimating the odds ratio, ranging from 1.5 to 2.1, and to a loss of power equivalent to a reduction in the number of subjects by a factor of 5 to 10. Analysis of systematic discrepancies between exposure assessments of the experts and the JEM showed that they were clustered with some job categories and arose from different sources: 1) inadequate job descriptions, related to the codification system adopted and necessitating the gathering of information at the individual level; 2) true disagreements between JEM and experts regarding the definition of solvent exposure.(ABSTRACT TRUNCATED AT 400 WORDS)

Case-Control Studies↗
PubMed1993

Relationship between birthweight and occupational exposure to cytostatic drugs during or before pregnancy.

The birthweight of babies whose mothers were exposed to cytostatic drugs during pregnancy was compared with that of infants whose mothers were not so exposed. The study was conducted in four French hospitals and covered 420 singleton live births to 466 women. One hundred and seven of the 420 births were exposed before or during pregnancy; 298 were not. Information about exposure was not available for the other 15. The mean birthweight of the babies of exposed mothers was 85 g lower than that of infants of unexposed mothers, but the difference was not statistically significant (95% CI -192.2-22.2 g). When gestational age and conventional risk factors were taken into account, the adjusted difference in the means of the birthweights was -56 (95% CI -155.1-43.1) g.

Adult↗
PubMed1990

Hematological findings among styrene-exposed workers in the reinforced plastics industry.

A cross-sectional survey of hematological parameters was carried out among 221 workers exposed to styrene in the reinforced plastics industry and 104 controls. Styrene exposure was assessed in both groups by monitoring urinary excretion of styrene metabolites (i.e. mandelic and phenylglyoxylic acids) in post-shift urinary samples collected over five consecutive days. Blood tests were performed with the same counter for all subjects. Information on factors liable to affect hematological parameters was collected from personal questionnaires completed by the workers. Urinary excretion of styrene metabolites varied from 15 to 3740 mg/g creatinine. Exposed subjects exhibited significantly lower mean values of neutrophils and mean corpuscular hemoglobin concentration (MCHC) than controls, and significantly higher mean values for monocytes and mean corpuscular volume. A dose-effect relationship was found for MCHC which decreased with urinary metabolite concentrations. These results remained statistically significant for all parameters after adjustment for age, sex, tobacco and alcohol consumption, place of residence (rural or urban) and time of blood sampling (morning or afternoon) with the exception of neutrophils whose relationship with exposure was essentially explained by smoking. These results are suggestive of a direct effect of styrene-exposure--in the range considered--on the statistical distribution of some hematological parameters.

Adult↗
PubMed1990

Risk of spontaneous abortion among nurses handling antineoplastic drugs.

The purpose of the study was to evaluate the frequency of spontaneous abortion in two groups of women. One group consisted of women regularly involved in the preparation of cancer chemotherapy perfusions and therefore considered to be exposed to cytostatic agents; the other consisted of women not occupationally exposed to such agents. The study was carried out in four French hospitals. Four hundred and sixty-six women were involved; 534 pregnancies were described in which 139 were exposed and 357 were unexposed. The results showed that the frequency of spontaneous abortion was 26% for the exposed pregnancies and 15% in the unexposed ones (odds ratio 2.0). These results do not seem to be due either to the classic risk factors of spontaneous abortion (age, cigarette consumption during pregnancy, pregnancy order) (adjusted odds ratio 1.7) or to possible errors concerning the retrospective evaluation of prior gynecologic and obstetric history.

Abortion, Spontaneous↗
PubMed1989

Assessing the significance of the correlation between two spatial processes.

Modified tests of association based on the correlation coefficient or the covariance between two spatially autocorrelated processes are presented. These tests can be used both for lattice and nonlattice data. They are based on the evaluation of an effective sample size that takes into account the spatial structure. For positively autocorrelated processes, the effective sample size is reduced. A method for evaluating this reduction via an approximation of the variance of the correlation coefficient is developed. The performance of the tests is assessed by Monte Carlo simulations. The method is illustrated by examples from geographical epidemiology.

Adult↗
PubMed1987

Comparison of relative risks obtained in ecological and individual studies: some methodological considerations.

This paper is concerned with the problem of estimating relative risks from ecological correlation studies. In the first part, some of the biases encountered when analysing aggregated data are discussed and in particular attention is focused on the shape of the dose-response relationship obtained from aggregated and non-aggregated data, on the need for extrapolation and on the scale of aggregation. In the second part some empirical observations are made on these points by means of four examples concerning the relative risk between smoking and different pathologies. The estimates of relative risks derived from French geographical data and from case control or cohort studies are compared. The performance of ecological studies is discussed with respect to the strength of the risk factor considered, the geographical distribution of counfounding factors and the adjustment of different models.

Adult↗
PubMed1979

[Organic micropollution of drinking water].

This work is about organic micropollution of waters sampled at the flowing in and out of three treatment stations. Micropollutants are obtained by chloroformic extraction. It is shown that the extracts have biological effects which can be measured by in vitro and in vivo assays. The treatments reduce the total amount of extractible substances but they induce modifications in their chemical composition and their biological activity. These observations allow to precise how the problem of an eventual health effect of organic micropollution could be approached.

Animals↗