Abstract
In Reply. —Dr Winkelstein raises the possibility of selection bias in our analysis of CD4 lymphocyte decline in the ALIVE cohort of IVDUs. This bias must always be a serious concern in any longitudinal study; for this reason and because the decline in CD4 lymphocytes in our cohort of IVDUs was lower than that reported by others, we looked for evidence of significant bias in our original analysis, as Winkelstein notes. However, we did not find such evidence, and we concluded that while the possibility of selection bias could not be completely excluded, a large bias did not appear likely, for the reasons already stated. We have recently updated the analysis of CD4 lymphocyte changes in our cohort based on an additional year of follow-up. Eighteen-month follow-up data are now available for 537 (85.7%) of the 627 cohort members, and the median rate of CD4 lymphocyte change is -7.4/μL per
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