Web-based tracking methods in longitudinal studies

•Online resources reduce attrition in longitudinal, program evaluation studies.•Success rates in locating former program participants varied from 8.7% to 92.8%.•Characteristics of the participants is the most important variable for rate variation.•Use of multiple websites reduces attrition for difficult-to-locate participants.•Six lessons learned are offered, including prospective participant involvement. The use of online resources to reduce the attrition of program participants in longitudinal studies is examined. Higher-risk individuals, those involved in illegal activities, and females with last name changes are typically more difficult to locate. The effectiveness of using online resources for these participants is addressed. These resources include social networking sites, people-finder search engines, telephone and address directories, judicial records, and death records. The strengths and limitations of these resources are presented and discussed. Longitudinal studies using these resources are examined to evaluate their successful follow-up rates. The results of these studies indicate that participant characteristics are more important to successful follow-up than the length of time since participation or sample size. The use of multiple online sites increased follow-up rates, especially for those who are typically difficult to locate. The variables and websites to consider are discussed, and six lessons learned are offered. The prospective use of online participant involvement is especially important for successful longitudinal evaluation and program planning.