experiment to choose the survey mode for the impact evaluation’s endline survey (conducted a few months later).

As we show in Figure 1, we enrolled a total of 6,258 individuals for the main impact evaluation.<sup>9</sup> These individuals were recruited through three channels: Facebook, the implementing partner’s network, and WhatsApp messages sent to customers of Tigo, the largest cell phone provider in El Salvador.<sup>10</sup> These individuals received a link to an enrollment survey in August 2020.<sup>11</sup> Only 4,718 individuals met the eligibility criteria for the impact evaluation and were allowed to enroll in the study.<sup>12</sup> After enrollment, we contacted them for a baseline survey between August and September 2020, and collected baseline data from 3,103 individuals (66 percent) for the impact evaluation.<sup>13</sup> In October 2020, we conducted the midline survey with a group of 599 randomly selected individuals out of the 4,718 enrolled in the impact evaluation.

The survey-mode experiment aimed to evaluate the relative convenience of the two survey modes based on four criteria: (i) response rate, (ii) changes in composition of respondents, (iii) quality of responses, and (iv) cost.<sup>14</sup> We calculate the response rate as the percentage of contacted individuals who complete the survey. We assess changes in the composition of respondents by measuring changes in their report of stress and attitudes toward violent parenting practices. We measure the quality of responses by checking the consistency of responses in the midline survey against those reported in the baseline and endline surveys. Finally, we use data on the monetary cost of contacting individuals through the two channels under analysis.

To conduct the survey-mode experiment, we first randomly selected 300 individuals from each treat9These were selected by Tigo by random digit selection and by also making sure that individuals were not residing in the same address or vicinity of the same address. This avoids a potential treatment contamination concern.

> 10Table A7 presents data on the channel used to recruit our sample. Most participants in the midline survey (and the impact evaluation) were recruited through Tigo’s client network. A similar recruitment process could be replicated in contexts with a high mobile-phone ownership rate, such as El Salvador, where 81 percent of the population owns a mobile phone.

11 The enrollment survey questions and consent form are available in this link.

12The eligibility criteria to participate in the impact evaluation were being between 18 and 45 years of age, living with at least one child eight years old or younger, having access to a mobile phone, and providing consent to receive digital messages and to participate in the study (Amaral et al., 2021).

> 13As explained in Amaral et al. (2021), 34 percent of enrolled individuals did not complete the baseline survey for different reasons, including did not provide a correct phone number, were not able to be reached after several attempts, and decided not to participate in the survey.

14The following section describes in more detail how we measure these three variables.

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