Considerations for TPP Evaluations with Multiple Follow-Up Assessments

This brief provides guidance for analyzing repeated measures teen pregnancy prevention (TPP) impact evaluations with multiple follow-up assessments. Research studies for TPP programs often include multiple follow-up assessments designed to test the differences between treatment and control (or comparison) groups over time. This brief discusses four primary decision points for evaluators and researchers to consider when analyzing data for studies with multiple follow-up assessments: 

1. Accounting for baseline measures
2. Choosing between separate or longitudinal models
3. Treating time as discrete or continuous
4. Accounting for within- person correlation

Discussions in this brief are best suited for evaluators and researchers who have some familiarity with statistical modeling and with the TPP Evidence Review Standards. Additional details and references for audiences interested in a deeper technical understanding are provided in footnotes throughout the brief and in an accompanying technical appendix.