Agreement between self-reported and pharmacy data on medication use in the Northern Finland 1966 Birth Cohort.

Objective: To compare self-reported (SR) medication use and pharmacy data for major psychoactive medications and three classes of medications used for different indications, and to determine the socio-economic factors associated with the congruence.

Methods: Postal questionnaire data collected in 1997 were compared with the register of the Social Insurance Institution of Finland on the reimbursed prescriptions purchased during 1997. Altogether 7625 subjects were included in this study. Drugs were categorized according to the Anatomical Therapeutic Chemical (ATC) system.

Results: Kappa values were 0.77, 0.68, 0.84, 0.92 and 0.55 for antipsychotics, antidepressants, antiepileptics, antidiabetics and beta-blocking agents, respectively. Prevalence-adjusted and bias-adjusted kappa values were almost perfect (0.98-1.00). Reliability of antipsychotics use was better for married subjects than for those who were not married; and of antidepressants use for highly educated and married subjects than for those who were less educated and were not married. Altogether 414 (5.4%) responders and 285 (7.1%) non-responders had used at least one of the selected medications.

Conclusion: Agreement between the SR and pharmacy data was moderate for psychoactive medication use. Even though data collected by postal questionnaire may underestimate the prevalence of medication use due to non-participation it can be assumed accurate enough for study purposes.