RT Journal
A1 Kerns SU, Pullmann MD, Walker S, Lyon AR, Cosgrove TJ, Bruns EJ
T1 SChool-based health center use and high school dropout rates—reply
JF Archives of Pediatrics & Adolescent Medicine
JO Archives of Pediatrics & Adolescent Medicine
YR 2012
FD July 1
VO 166
IS 7
SP 675
OP 677
DO 10.1001/archpediatrics.2012.553
UL http://dx.doi.org/10.1001/archpediatrics.2012.553
AB 
Treating time-varying variables as fixed can result in a systematic bias referred to as “time-dependent bias,”1 “immortal time bias,”2 or “survival bias.”3 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 operationalize at least 1 time-varying variable in the model.1