Abstract
Background There are significant challenges associated with studies of people released from custodial settings, including loss to follow-up in the community. Interpretation of findings with consideration of differences between those followed up and those not followed up is critical in the development of evidence-informed policies and practices. We describe attrition bias in the Prison and Transition Health (PATH) prospective cohort study, and strategies employed to minimise attrition.Methods PATH involves 400 men with a history of injecting drug use recruited from three prisons in Victoria, Australia. Four interviews were conducted: one pre-release (‘baseline’) and three interviews at approximately 3, 12, and 24 months post-release (‘follow-up’). We assessed differences in baseline characteristics between those retained and not retained in the study, using two-sample tests of proportions and t-tests.Results Most participants (85%) completed at least one follow-up interview and 162 (42%) completed all three follow-up interviews. Retained participants were younger than those lost to follow-up (mean diff − 3.1 years, 95% CI -5.3, -0.9). There were no other statistically significant differences observed in baseline characteristics.Conclusion The high proportion of participants retained in the PATH cohort study via comprehensive follow-up procedures, coupled with extensive record linkage to a range of administrative datasets, is a considerable strength of the study. Our findings highlight how strategic and comprehensive follow-up procedures, frequent contact with participants and secondary contacts, and established working relationships with the relevant government departments can improve study retention and potentially minimise attrition bias.
The risk of cancer among persons with a history of injecting drug use in Sweden – a cohort study based on participants in a needle exchange program
