This is the methodological appendix for "Investing in Single Mothers' Higher Education: National and State Estimates of the Costs and Benefits of Single Mothers' Educational Attainment to Individuals, Families, and Society." The Institute for Women's Policy Research's (IWPR) briefing paper, features findings from a study to quantify the individual and societal costs and benefits of single mothers' attainment of college degrees (see Reichlin Cruse et al. 2019). This work builds off of previous IWPR research on investments in single mothers' education (see Gault, Milli, and Reichlin Cruse 2018), adapting it to an analysis at the state level. In addition to the state-level focus, IWPR's 2019 briefing paper improves upon the previous report in several key ways: it estimates the impact of college education on lifetime public assistance receipt among single mothers (the previous report estimated the effect over a four-year period); it includes a new analysis of the impact of some college credit on outcomes among single mothers, even though they did not obtain a degree; and with the addition of the some college analysis, we are now able to estimate the full return on investment in support services for single mother students. These improvements, along with the remainder of the analysis, are discussed in greater detail in this appendix. [For the briefing paper, see ED612588.]