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Activity Number: 115
Type: Contributed
Date/Time: Monday, August 7, 2006 : 8:30 AM to 10:20 AM
Sponsor: General Methodology
Abstract - #305369
Title: Selection Bias Due to Immigration in Pharmacoepidemiologic Studies
Author(s): Henrik Stovring*+
Companies: University of Southern Denmark
Address: JB Winslows Vej 9A, Odense, 5000, Denmark
Keywords: pharmacoepidemiology ; selection bias ; waiting time distribution ; prevalence
Abstract:

In pharmacoepidemiology, a so-called run-in period is used often to determine treatment status at an index date. Individuals immigrating during the run-in period are, however, excluded from further analysis, as their treatment status cannot be determined. This may lead to selection bias. Using the recently developed waiting time distribution (WTD) method, which avoids use of a run-in period, the size of this bias is studied with respect to prevalence of use of antidiabetic drugs in the County of Funen, Denmark, from 1993--2003. The relative bias in prevalence estimates, due to the selection created by using a half-year run-in period, is found to be approximately 1% for each calendar year (range .73%; 1.36%), but when controlled for gender and age, this bias vanishes, except for ages under 40. Immigrants generally had a prevalence half the size of nonimmigrants.

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