Drug exposure risk windows and unexposed comparator groups for cohort studies in pharmacoepidemiology

TY - JOUR

T1 - Drug exposure risk windows and unexposed comparator groups for cohort studies in pharmacoepidemiology

AU - McMahon, Alex D.

AU - Evans, Josie M. M.

AU - McGilchrist, Mark M.

AU - McDevitt, Denis G.

AU - MacDonald, Thomas M.

PY - 1998/7

Y1 - 1998/7

N2 - Aim: To determine the appropriate size of risk windows in both exposed and unexposed subcohorts.Method: Data was taken from a previous study of upper gastrointestinal haemorrhage and perforation. The length of each prescription for NSAIDs was estimated. The risk was calculated for the duration of a prescription plus increments of -30, -25, ..., +115, +120 (i.e. 31 increments). Ten unexposed groups were re-sampled for each increment (stratified for age and sex), using the same lengths of risk window as the exposed group. Mean risks and rate-ratios were calculated (per thousand person-years).Results: The NSAID risk rose from 3.52 at -30 days to a peak of 5.82 at -15 days, and then decreased gradually to 2.83 at +120 days. Unexposed risk was variable for the negative increments, and decreased gradually from 2.16 at +0 days to 1.54 at +120 days. The rate-ratio rose from 1.55 at -30 days to a peak of 2.85 at -5 days, and then decreased to 1.85 at +120 days.Conclusion: Risk windows should be the same as (or slightly less than) the calculated length of a prescription. Lengthy windows should not be used for unexposed comparator groups (the exposed windows may be randomly allocated).

AB - Aim: To determine the appropriate size of risk windows in both exposed and unexposed subcohorts.Method: Data was taken from a previous study of upper gastrointestinal haemorrhage and perforation. The length of each prescription for NSAIDs was estimated. The risk was calculated for the duration of a prescription plus increments of -30, -25, ..., +115, +120 (i.e. 31 increments). Ten unexposed groups were re-sampled for each increment (stratified for age and sex), using the same lengths of risk window as the exposed group. Mean risks and rate-ratios were calculated (per thousand person-years).Results: The NSAID risk rose from 3.52 at -30 days to a peak of 5.82 at -15 days, and then decreased gradually to 2.83 at +120 days. Unexposed risk was variable for the negative increments, and decreased gradually from 2.16 at +0 days to 1.54 at +120 days. The rate-ratio rose from 1.55 at -30 days to a peak of 2.85 at -5 days, and then decreased to 1.85 at +120 days.Conclusion: Risk windows should be the same as (or slightly less than) the calculated length of a prescription. Lengthy windows should not be used for unexposed comparator groups (the exposed windows may be randomly allocated).

KW - Cohort study

KW - MEMO

KW - Pharmacoepidemiology

KW - Risk window

KW - Unexposed group

U2 - 10.1002/(SICI)1099-1557(199807/08)7:4<275::AID-PDS363>3.0.CO;2-N

DO - 10.1002/(SICI)1099-1557(199807/08)7:4<275::AID-PDS363>3.0.CO;2-N

M3 - Article

AN - SCOPUS:0031875549

SN - 1053-8569

VL - 7

SP - 275

EP - 280

JO - Pharmacoepidemiology and Drug Safety

JF - Pharmacoepidemiology and Drug Safety

IS - 4

ER -