Follow-up attrition in alcohol treatment studies: Is 'no news' bad news, good news or no news?

It is generally thought that loss of data for a substantial portion of subjects in alcohol treatment follow-up studies positively biases outcome results. However, the data upon which this claim has been based relates to subjects who are initially difficult to locate but who were later found, and not subjects who were actually lost to follow-up. Similarly, data are lacking regarding the functioning of subjects who drop out of a study before the completion of follow-up. In this paper some limited data are presented from an alcohol treatment outcome study which suggest that there may be an important difference between subjects who are lost to follow-up and those who voluntarily terminate their participation in follow-up. Specifically, those subjects lost to follow-up were functioning poorly prior to being lost, whereas at the time of termination, those who discontinued follow-up were functioning about as well as other subjects in the study. It is suggested that the use of multiple follow-up contacts can provide additional data on subjects who are eventually lost to or drop out of follow-up.