This report is a technical supplement to the 15-month impact report for the Building Strong Families (BSF) evaluation, a study that explored the effectiveness of providing services to improve the relationships of unmarried parents. It provides additional detail about the research design, analytic methods, and variable construction that were used for the 15-month analysis. Chapter 1 begins with an overview of the research design. It then describes BSF sample intake procedures, including eligibility determination and the random assignment process. The eight local BSF programs enrolled couples into the study sample from July 2005 to March 2008. Across the eight programs, 5,102 couples were randomly assigned, with 2,553 assigned to the BSF group and 2,549 assigned to the control group. The following chapter provides details on how this research design was implemented, including the multivariate estimation methods, treatment of missing data, multiple comparison analysis, and statistical sensitivity tests. Chapter 3 details the measures of relationship quality used in the impact analyses and how the evaluation team approached impact analyses of those measures given that some are available only for intact couples, and Chapter 4 describes the other relationship outcomes examined, including measures of relationship status, attitudes toward marriage, and intimate partner violence. In addition, the chapter describes measures of parenting and father involvement included in the impact analysis. The final chapter provides a discussion of the subgroup analysis that was conducted to examine whether BSF was more effective for certain subgroups of couples. Numerous references, 23 tables, and 1 figure.