Nancy S. Padian, Charles B. Holmes
Evaluations of health-care programmes are only as good as the data and methods used, and as in all longitudinal research, loss to follow-up is among the prime spoilers. For cohort studies including randomised controlled trials, loss to follow-up attenuates the ability to examine outcomes or the effect of an intervention and predictors of these outcomes. Patient-level data from health facilities are subject to the same biases. Most patients are probably not lost at random and reasons for loss to follow-up could be inherently linked to the effectiveness of clinical services.