PHARMACOEPIDEMIOLOGY AND PRESCRIPTION High concordance between self-reported medication and official prescription database information Jari Haukka & Jaana Suvisaari & Annamari Tuulio-Henriksson & Jouko Lönnqvist Received: 8 February 2007 / Accepted: 6 July 2007 / Published online: 22 August 2007 # Springer-Verlag 2007 Abstract Objective We set out to compare the agreement between self-reported psychotropic medication use and information obtained from the administrative prescription database of the Social Insurance Institution of Finland. We compared the point prevalence of psychotropic medication use, and self- reported vs. register-based information on antipsychotic medication dosage. Methods The study population consisted of 905 partic- ipants from a population-based genetic study of schizo- phrenia, of whom 366 had schizophrenia spectrum disorder, 56 had bipolar spectrum disorder, and 483 were unaffected family members. Current medication use was obtained by interview and from the prescription reimbursement data- base. Agreement between data sources was compared using Cohen’ s kappa statistic and correlation coefficients. Results The agreement between the two sources was gener- ally good. Kappa values were best for lithium use (0.96; p <0.0001), followed by antipsychotics (0.87; p <0.0001) and antidepressants (0.77; p <0.0001). Agreement was lowest for benzodiazepines (0.42; p <0.0001). Correlation between antipsychotic medication dose estimates was 0.79 (95% CI 0.76–0.81). Conclusion The concordance between self-reported psy- chotropic medication use and information obtained from an official prescription database was good for most psycho- tropic drugs. More studies are needed to replicate results with other forms of medication and patient groups. Introduction Pharmacoepidemiology is the study of medication use and medication effects in populations. Pharmacoepidemiolog- ical studies often utilize data from official administrative individual-level prescription databases [1, 2, 11, 13, 14]. Because register-based observational studies are usually the only feasible study type in post-marketing surveillance, the validity of register data is very important when the quality of studies is being considered. Whether the focus of the study is drug use or drug effect, the quality of the findings is entirely dependent on the quality of the original data. Individual-level prescription databases provide informa- tion on how each drug is utilized. However, even determining the point prevalence of the use of a drug from prescription data can be difficult [1]. For the determination of prevalence, a number of assumptions must be made, and the effects of assumptions are not usually carefully evaluated. One of the most important assumptions is that after purchase the drugs are utilized as prescribed. Usually, dose is assumed to be one international standard daily defined dose per day. Most methods entail assigning a period of usage to each prescription record [8]. The point prevalence on a given day is then estimated from the number of persons who have a prescription whose period of usage crosses this date. Usually, noncompliance or irregular patterns of periods on and off cannot be taken into account. To improve the quality of register-based pharmacoepidemiological studies, possible sources of bias and other factors that could distort informa- tion obtained from administrative registers should be carefully studied. One way to scrutinize such biases is to compare register-based data with data obtained from self- reports, or from plasma concentrations of medications. When the utilization of medicines is estimated on the basis of an administrative register, there are several sources Eur J Clin Pharmacol (2007) 63:1069–1074 DOI 10.1007/s00228-007-0349-6 J. Haukka (*) : J. Suvisaari : A. Tuulio-Henriksson : J. Lönnqvist Department for Mental Health and Alcohol Research, Mannerheimintie 166, 00300 Helsinki, Finland e-mail: jari.haukka@ktl.fi