they appear to be minor for less sensitive survey questions (Di Maio and Fiala, 2020; Garlick et al., 2020; Himelein, 2016). The social similarities of the interviewer and the respondent, or lack thereof, are a key factor in how much interviewers affect both responses and participation in the survey, with language playing a crucial role (Di Maio and Fiala, 2020; Randall et al., 2013).

As with in-person surveys, choosing, training, and supervising interviewers well is an important aspect of phone survey design. In addition to the skills that are needed specifically for phone surveys, such as desirable phone etiquette and, preferably, experience with the CATI application that is being used to record data (or other selected phone survey implementation mode), familiarity with the content of the questionnaire can be of great value. In cases of recontact surveys, the interviewers employed in the baseline survey may hold valuable knowledge of the questionnaire content, making training more efficient, as well as some developed relationships with respondents, which can also help reduce nonresponse.

## _Training and supervision_

To limit the impact of interviewer effects, thorough and consistent training of both interviewers and supervisors is essential. Training for phone surveys, when feasible, can be conducted in person similar to the manner in which traditional in-person surveys are administered. In cases where in-person training is not a possibility, such as in the case of the LSMS-supported HFPS surveys, Amankwah et al. (2020) and Glazerman et al. (2020) recommend the use of various remote learning tools, including videos, web-based tutorials, and quizzes.

In the case of CATI implementation, quality control and supervision may extend beyond the team supervisors themselves. The use of audio recordings of phone-based interviews, potentially on a random sample of interviews and/or random segments of interviews, can allow survey managers at headquarters to review interviewer skills, explanations, and interactions with respondents, enabling the identification of behaviors that are outside the norm or are not as intended by survey management. These audio audits can also allow cross-referencing of data points in the recorded data and the audio exchange, as a further quality control measure. In the LSMS-supported HFPS surveys, audio audits were employed in Ethiopia and Nigeria and were found to be effective in identifying weakly performing interviewers, to which additional supervisory efforts were directed (Gourlay et al., 2021).

# 5. Cost considerations

Cost considerations are central to every survey operation. Perhaps the most appealing feature of phonebased survey implementation in low-income contexts is the reduced cost relative to traditional in-person data collection. Data for the World Bank’s LSMS-ISA and High-Frequency Phone Surveys on COVID-19 offer a useful cost comparison of in-person and phone survey modes, for the same countries, at about the same time and on overlapping samples (Table 3).

When comparing _costs per completed interview_ , in-person surveys are about 30 times as expensive compared to phone surveys. In this sample of countries, the cost per in-person interview ranges from 230 USD per household in Burkina Faso, to 409 USD in Tanzania.<sup>10</sup> For the same countries, the range of per interview costs for phone surveys is from 8 USD in Tanzania to 12 USD in Malawi. Comparing the _cost per question_ substantially reduces these cost differences, with phone surveys generally appearing to be 3-4

> 10 See Kilic et al. (2017) for a more comprehensive review of the cost of in-person household surveys.

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