The potential for Simpson's paradox in drug utilization studies.
OBJECTIVE
Simpson's paradox is a type of severe confounding wherein a confounding variable changes the direction of an association.


METHODS
This article demonstrates Simpson's paradox with three cohorts of naproxen users (new users, chronic users, and combined users) who were compared on the age/sex distribution of further naproxen use. Hypothetical new and chronic user populations were constructed with the same proportions for further naproxen use as their original counterparts.


RESULTS
The hypothetical combined population showed an age/sex distribution opposite to that of the original combined population.


CONCLUSIONS
This example of Simpson's paradox is a significant finding as many drug utilization studies do not distinguish between component populations.
Neutel
C I
CI
Health Canada, Ottawa, Ontario, Canada.
D000328:Adult; D017677:Age Distribution; D000368:Aged; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage*; D002170:Canada; D015331:Cohort Studies; D015986:Confounding Factors, Epidemiologic; D011307:Drug Prescriptions / Q000706:statistics & numerical data*; D004363:Drug Utilization / Q000706:statistics & numerical data; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009288:Naproxen / Q000008:administration & dosage*; D012042:Registries; D012680:Sensitivity and Specificity; D017678:Sex Distribution; D013997:Time Factors
D000894:Anti-Inflammatory Agents, Non-Steroidal; D009288:Naproxen