TY - JOUR T1 - A characterisation of patient drop outs in a cohort of HIV positive homosexual/bisexual men and intravenous drug users JF - Journal of Epidemiology and Community Health JO - J Epidemiol Community Health SP - 66 LP - 67 DO - 10.1136/jech.55.1.66 VL - 55 IS - 1 AU - W K Poole AU - R Perritt AU - K B Shah AU - Y Lou AU - J Turner AU - P Kvale AU - P C Hopewell AU - J Glassroth AU - M Rosen AU - L Reichman AU - J Wallace AU - the Pulmonary Complications of Immunodeficiency Virus Infection Study Group Y1 - 2001/01/01 UR - http://jech.bmj.com/content/55/1/66.abstract N2 - Enrollees in a study who cease participation for one reason or another can create problems for those who analyse and interpret the data. These problems include loss of statistical power, bias in the study results, and lack of generalisability of the study findings. Whether the study is a clinical trial or an observational study these problems may exist. In trials, for example, non-random withdrawals may compromise the comparability between the treatment groups and hence introduce a bias and in observational studies selective withdrawal may limit the generalisability of the study results. Much has been written about the consequences of non-random withdrawals and some authors have offered statistical techniques that can effectively adjust for the resulting bias if certain assumptions are met. Although it is not generally possible to compensate for all of the problems created by attrition, certain considerations like statistical power and adequate representation of important subgroups can … ER -