Doing more than just acknowledging attrition at follow-up: a comment on Lu, Cheng, and Chen (2013).

Lu, Cheng, and Chen (2013 ) faced one of the most common challenges encountered in longitudinal studies: follow-up attrition. Using a correlational prospective design, 464 volunteers completed a questionnaire that measured the constructs of the theory of planned behavior, and subsequently 154 of them provided physical activity data at a 6-month follow-up. The proportion of participants (66.8%) for whom the investigators were not able to gather information on the behavioral outcome at follow-up may reflect a form of selection bias that may affect both the validity and generalizability of study results. Lu, et al.'s (2013 ) study is used here to explore the implication of follow-up attrition on the results and inference, to review what information should be reported in a scientific paper in such situations, and to give practical tips to handle follow-up attrition.