Original article
Factors associated with self-reporting of chronic health problems in the French GAZEL cohort

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Abstract

The objective of this study was to examine factors associated with self-reporting of chronic health problems. The self-reports were obtained from a questionnaire sent by mail to the French GAZEL cohort, composed of workers of a French company. The disorders reported in the questionnaire were compared with diagnoses from the sick-leave database of the company. Associations between self-reporting and characteristics were studied by multiple logistic regression analyses. Three types of characteristics were analyzed: individual, methodological and disorder-related (i.e., prevalence of chronic disorders in the general population, probable disability and probable life risk scores). In 1992, the cohort consisted of 16,534 subjects aged 38 to 53 years. The reporting rate (number of self-reports in the questionnaire divided by number of records in the sick-leave database for the disorder considered) varied from 8.9% to 100%. Self-reporting was associated with individual characteristics (gender, family status, place of residence, annual number of sick days and sick leaves), disorder-related characteristics (probable disability, prevalence) and methodological characteristics (precision of the formulation, delay between the last sick-day and the patient report). By body system, the characteristics associated with self-reporting varied greatly but the annual number of sick days, probable disability and precision of formulation were the variables which remained most often in the models. These characteristics should be particularly taken into consideration in the interpretation of epidemiological results based on self-reporting.

Introduction

The collection of health data in epidemiological studies is often based on self-reporting by participants, because of the relative simplicity and low cost of this method. Nonetheless, different authors have shown that the validity of this type of data raises questions and they have stressed the extreme variation in the quality of reporting, according to the type of disorder 1, 2, 3, 4, 5, 6. Different individual characteristics, age 2, 5, 6, 7, gender 5, 6, 7, occupational status [2], educational level 2, 5, 6, 7, degree of urbanization [5], mobility limitations [6] and recent contact with the general practitioner [6], are associated with reporting and may explain its variations according to disorder as well as the variations from one study to another. The role of some methodological aspects of surveys has also been studied; these include the conditions under which the questionnaire is completed (e.g., the presence of an investigator during the interview vs. self-administrated questionnaires, the presentation of a list of disorders vs. general questions without mentioning specific disorders) 3, 8, 9, and the precision of the medical terminology used in the questionnaire 2, 3, 10. Few authors, however, have studied these types of factors simultaneously. Gross et al. [4] showed the separate effect of the number of disorders per participant and age on reporting. Kriegsman et al. [6] demonstrated the influence of gender, age, mobility limitations and recent contact with the general practitioners on the level of accuracy.

The GAZEL cohort, composed of more than 20,000 volunteers employed at the French national electricity and gas company, was established in 1989. The incidence and prevalence of their chronic health problems are measured from responses to a questionnaire mailed to them annually. The objective of this present study is to examine factors associated with self-reporting of chronic health problems in this cohort.

Section snippets

Study population

The participants in the GAZEL cohort are volunteers working for Élecricité de France-Gaz de France (EDF-GDF), the French national utility company. The company employs roughly 140,000 workers in a range of socio-demographic categories, distributed geographically throughout France.

Since 1989, the GAZEL cohort has been under study by the National Institute of Health and Medical Research (Institut National de la Santé et de la Recherche Médicale, INSERM). Initially it included 20,625 participants:

Results

The comparison between the reported disorders in the 1992 questionnaire and the sick-leave data dealt with 3972 health problems of 3122 participants. The first stage of the selection procedure showed that 16,534 participants were living in continental France and had completed the 1992 questionnaire. Of these, 6542 (i.e., 39.6%) had a total number of 11,952 sick leaves in 1991. The second stage of the selection reduced the number to 7106 sick leaves (i.e., 59.5% of the total). We eliminated the

Discussion

This study found that the reporting rates for different disorders varied greatly. The rates by item ranged from 8.9% to 100%. The range of variation was lower but still high when looking at the rates by body system, from 35% to 91.7%. The multiple logistic regression analyses showed that the three types of characteristics studied were associated with self-reporting. By body system, annual number of sick days, probable disability and precision of formulation were the variables which remained

Acknowledgements

The authors express their thanks to EDF-GDF, especially to the Service des Etudes Médicales. They also thank Mr. Busson and Drs. Com-Ruelle, Lecomte, Le Fur and Sermet, from CREDES, who kindly gave access to the indicators derived from the French INSEE-CREDES National health survey.

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