Revisiting the washout period in the incident user study design: why 6-12 months may not be sufficient

• Published in: Journal of comparative effectiveness research Vol. 4; no. 1; pp. 27 - 35
• Main Authors: Roberts, Andrew W, Dusetzina, Stacie B, Farley, Joel F
• Format: Journal Article
• Language: English
• Published: England Future Medicine Ltd 01.01.2015
• Subjects: Adolescent; Adult; Analysis; Antidepressants; Antidepressive Agents - administration & dosage; Comparative Effectiveness Research; Databases, Factual; Female; Humans; Hypoglycemic Agents - administration & dosage; Hypolipidemic Agents - administration & dosage; incident user design; Insurance Claim Review; Male; methods; Middle Aged; Pharmacoepidemiology; Pharmacoepidemiology - methods; Research Design; secondary databases; selection bias; Time Factors; United States; selection bias; research design; incident user design; methods; comparative effectiveness research; pharmacoepidemiology; secondary databases
• ISSN: 2042-6305; 2042-6313; 2042-6313
• DOI: 10.2217/cer.14.53

The purpose of this study was to describe how washout period duration affects the size and accuracy of retrospective incident user cohorts. MarketScan commercial claims data from 2007 to 2010 were used and included adults with an antihyperlipidemic, antidiabetic or antidepressant claim in 2010. Incident user cohorts using 3-, 6-, 12-, 24- and 36-month washouts were created and changes in sample size and incident user misclassification were described. The 6- and 12-month washouts excluded 75 and 85% of the samples, respectively. Half of subjects in the 6-month washout cohorts were actually prevalent users, and the 12-month washout period resulted in 30% misclassified. Using common washout periods of 6-12 months may insufficiently address prevalent user bias in large commercial claims databases.