A replicable model for achieving over 90% follow-up rates in longitudinal studies of substance abusers

Abstract

The goals of this paper were to: (a) discuss the interface between dominant behavioral patterns of substance users and the development of a follow-up management model, (b) describe the components of the model, (c) present data regarding its effectiveness, (d) estimate the number of contacts for various follow-up rates, (e) explore the generalizability of the model across sub samples, and (f) present client outcome data that underscore the potential negative impact of low follow-up rates. The model has been used to follow-up over 12,000 research participants yielding over a 95% follow-up rate across seven studies (with over 90% completed within +/-14 days of their anniversary date). Using data from two of these studies (n = 2010, n = 632), 22 contacts or less captured 70% of the participants while 33 or 38 contacts or less captured 90% in the first and second studies, respectively. When outcome variables were compared based on 70% versus 90% follow-up, the results varied by study and within study. An examination of the effect of attrition on validity in these two samples demonstrated that even the traditionally acceptable 30% level of attrition can result in significant bias and that the nature of the bias is unpredictable.

Fig. 1

EVMC Follow-up Protocol. This figure shows the EVMC protocol for recruiting, verifying locator information, tracking and getting people to a single interview at 3 months. (Modifications for subsequent waves or longer durations are discussed further in the text.)

Fig. 2

Percent of completed interviews by number of contacts. This figure shows the cumulative percent of interviews completed by number of contacts for each study. The tables that follow compare subgroups on the number of contacts to reach 70% and the maximum; and on the mean of several variables for those requiring more or less contacts than the 70th percentile (marked on the figure).