al., 2021). At the other extreme, respondents may also feel burdened if they are contacted too frequently. Garlick et al. (2020) found that phone interviews at a weekly frequency did not induce persistent changes in respondent reporting nor increase permanent attrition but did increase the incidence of missed interviews among microenterprise owners in South Africa. In contrast, Schündeln (2018) finds panel conditioning effects, whereby reported consumption levels are correlated to the number of interviews, for households visited up to 10 times per month during the Ghana Living Standards Measurement Study.

Incentives are key to increase participation rates in phone surveys and were provided in the vast majority of phone surveys discussed in this paper, including those implemented at a national scale. There is a common understanding that monetary payment is important to compensate participants for their opportunity cost of time as well as the cost of airtime and electricity that a phone conversation entails (Glazerman et al., 2020). Furthermore, incentives are provided to encourage engagement in future interviews and are found to increase cooperation and response rates (Gibson et al., 2019; Glazerman et al., 2020; Gourlay et al., 2021; Singer and Ye, 2013). LSMS-supported HFPS provided airtime-based incentives of between $0.70 and $1.83. Gibson et al. (2019) found little importance of the exact amount of the incentive, though Singer and Ye (2013) suggest incentives exhibit diminishing marginal returns as the amount increases. According to a number of studies, survey incentives, ranging in size from $0.10 to $3.00, increase response rate by around 5 percentage points, although this effect ranges from 2 to 10 percentage points depending on context and incentive size (Ballivian et al., 2015; Gibson et al., 2019; Glazerman et al., 2020).

## _Respondent contact protocols and privacy_

Carefully planning how and when to contact survey respondents is another way to reduce burden, increase cooperation and counteract attrition. Özler and Cuevas (2019) significantly increased recontact rates among a sample of refugees in Turkey by increasing the number of call attempts, spacing the call attempts appropriately, and reaching respondents in the evenings and weekends. Mathur (2020b) finds similar results when attempting to reach households in rural India. For agricultural data collection, deciding the dates and times to contact respondents requires that survey designers have information on the work schedule over several months of a typical agricultural household or holding. This informs the design decision of when to ask about specific farming activities, while also helping to understand when farmers will have time to participate in a survey.

Ensuring respondent privacy over the phone is very difficult (Glazerman et al., 2020). Calls to agricultural households can attract attention from other household members or non-household members, threatening respondent privacy and potentially biasing responses. This issue is more acute when sensitive questions are part of the survey, which may include questions on land rights and tenure. Highly sensitive questions, such as on violence against women and girls, cannot be collected in a safe fashion remotely and require a different approach (UN Women and World Health Organization, 2020).

# 4.3. Interviewer effects

Interviewers can also affect respondent behavior and data quality regardless of survey mode. Evidence of interviewer effects in surveys has been widely documented (West and Blom, 2016). Randall et al. (2013) show in an African context that interviewer behavior and characteristics can have an impact on the pattern of nonresponse. This is because interviewers often need to convince respondents to participate which requires considerable social skills. Interviewer behavior and characteristics can also affect, and bias, survey responses. Such effects appear to be meaningful for types of questions deemed sensitive though 20