International Journal of Epidemiology, Vol 28, 514-520, Copyright © 1999 by International Epidemiological Association
MW Langendam, HJ van Haastrecht and EJ van Ameijden
BACKGROUND: Epidemiological studies among drug users are often based on
retrospective self-reports. However, among others, memory failure, being
under the influence of drugs, psychopathology, misunderstanding of
questions and socially desirable answering may generate inaccurate
reporting. METHODS: This study validated self-reported current (methadone
dosage) and medium-term (main location of methadone dispensing and
frequency of methadone programme attendance over the previous 4-6 months)
aspects of methadone treatment in the Amsterdam AIDS cohort study among
drug users, using data of the Central Methadone Register. In addition to
descriptive measures, logistic regression analysis was used (adjusted for
intra-individual correlation) to identify subgroups with incorrect
reporting. Data collected at 4406 visits of 505 cohort participants were
analysed. RESULTS: Current methadone dosage was accurately reported
(unweighted kappa [kappa]: 0.94, weighted kappa [kappa W]: 0.97). A low
methadone dosage, short duration of school education and depressive or
euphoric mood during the interview were significant and independent
predictors of incorrect reporting of methadone dosage. For main location of
dispensing kappa was 0.82, for frequency of programme attendance kappa was
0.53 and kappa W 0.87. There was a tendency to reporting the extreme
answering categories. Infrequent programme attendance was the only
significant predictor of incorrectly reporting frequency of programme
attendance. CONCLUSIONS: Drug users are able to give valid self-reports in
a setting where social desirability does not play an important role. The
main reasons of incorrect reporting were impaired cognitive functioning,
memory failure and misunderstanding of questions.
ARTICLES
The validity of drug users' self-reports in a non-treatment setting: prevalence and predictors of incorrect reporting methadone treatment modalities
Municipal Health Service, Division of Public Health and Environment, Amsterdam, The Netherlands. mlangendam@gggd.amsterdam.nl
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