to establish eligibility. Overall, the census listing contains data from 8,572 adolescents from 4,341 households. Our baseline survey sample consisted of randomly selected 2,393 households that were stratified by community cluster and adolescent gender.

The main source of data we use for the evaluation is three rounds of individual-level surveys administered to both adolescents and their parents: one baseline, and two follow-up surveys (midline and endline). The baseline survey was conducted from February to July 2018 just before program implementation started. The midline survey was administered between February 2019 and January 2020 - after approximately half of those assigned to the _Choices_ training had completed the training. The endline survey was completed between September 2020 and October 2021, after all _Choices_ training and _EMB_ sessions were completed and after a coronavirus government-mandated lockdown period had been removed in Somalia.<sup>29</sup> The follow-up surveys were timed to take place approximately 6 months and 2 years post-intervention. To participate in the surveys, written or verbal consent, depending on literacy level, was obtained from parents or guardians, as well as from the adolescents themselves. Surveys were translated into Somali language and data collection took place through face-to-face interviews with enumerators. Wherever possible, the enumerator was from the same region as the adolescent. Questions and scales were piloted extensively and enumerators were trained carefully in the wording of the questions and how to appropriately interact with young adolescents.

Each respondent was interviewed in private and adolescents and parents were asked two different questionnaires. Typically the adolescent’s mother and/or father were interviewed for the adult survey.<sup>30</sup> At baseline, adolescents were asked to provide information on basic demographic characteristics (such as age, education and health), attitudes towards gender equality and perceived community norms (particularly on the role of women in- and outside of the household), opinions on marriage, hope and aspirations for the future, as well as their answers to a strengths and difficulties questionnaire (SDQ).<sup>31</sup> Adolescents were also asked to provide information on the quality of the relationship with their parents, time use, and their involvement in household chores. Parents were asked about their own marriage history, decision-making power and attitude towards intimate partner violence (IPV), gender attitudes and perceived norms, behavioral characteristics (conformity, risk preferences), aspirations for their children, and opinions on FGM and early marriage.<sup>32</sup> The midline and endline questionnaires were very similar to the baseline but collected additional information 29The COVID-19 pandemic reached Somalia in March 2020 and the country went into lockdown for several months. In July 2020 most of the government restrictions in Somalia had been lifted and schools reopened in August 2020. The lockdown also explains the relatively long survey period as survey teams tried to match the timing of surveys to the timing of the rollout of the intervention in each of the 6 districts.

> 30The respondent for the adult module was typically one or both parents or guardians. Enumerators were instructed to survey the mother and whenever possible, the father too. The baseline sample consists of 57% of households with one female respondent, 9% with one male respondent and 34% with both a female and a male respondent. Data is representative of mothers for all rounds of the survey. However, data from fathers should be considered a more selective sample as it was difficult to track and survey fathers for all rounds.

> 31Scales to measure attitudes and mental health outcomes were changed from a 3-point Likert scale at baseline to agree/disagree options in the follow-up surveys to make it easier for adolescents to respond accurately. In the Appendix we detail the individual statements in the attitudes index and present the Cronbach’s alpha to test for scale reliability (Cronbach’s alpha of the gender attitudes index is 0.798).

> 32Parents were also asked to provide basic information on the household including demographic information, plus food security, household assets and consumption modules.

10