School-based health center use and high school dropout rates - Reply

摘要

Treating time-varying variables as fixed can result in a systematic bias referred to as "time-dependent bias,"1 "immortal time bias, " or "survival bias. " This is a common analytic error; in a review of publications from 9 top medical journals from 1998 to 2002, of 127 studies that used survival analysis with time-dependent variables, 41 % (52 studies) were susceptible to time-dependent bias because they did not appropriately operationalizc- at least 1 time-varying variable in the model.