M., Solomon, W., Singh, Y. et al, 2009, Ballivian et al 2015, Dabalen et al, 2016, Lau et al, 2019, (Fu et al, 2015, Himelein and Kastelic, 2015 and Leo et al, 2015). Phone surveys have an array of advantages over typical F2F surveys, primary among them is cost. F2F surveys require interviewers to travel to the household’s or individual’s location to conduct the interview which introduces substantial travel and logistical costs, particularly for national surveys. On the other hand, phone surveys require no travel and interviewers can conduct all their calls from one location. In the era of the coronavirus pandemic, another advantage of phone surveys has been realized in that it eliminates the need for contact with others (either through travel or conducting the F2F interview) and thereby has minimal risk of COVID-19 exposure for interviewers and respondents alike. This advantage contrasted with the COVID-19 risks associated with F2F data collection has led to a proliferation of phone surveys in the developing world during the coronavirus pandemic.

However, phone surveys also suffer from some disadvantages when compared to F2F surveys. One of the main disadvantages (and the focus of this study) is that phone surveys often suffer from coverage and nonresponse bias that erode the representativeness of the interviewed sample. **Coverage bias** results from the typical exclusion of the segment of the population that does not have access to a telephone (either mobile or landline). Although mobile phone penetration is increasing in developing countries, in many countries there is still a sizable share of the population that lacks access and would not be represented in typical phone survey samples. There are likely substantial differences between this uncovered portion of the sample and the covered portion that will introduce bias in the results obtained.

Phone surveys also commonly suffer from **nonresponse bias** whereby the pool of sampled households or individuals who are not successfully interviewed are substantially different from those interviewed. Nonresponse is a common feature of any survey including F2F surveys, but the potential for nonresponse is typically substantially higher for phone surveys. One reason nonresponse is often higher for phone surveys is the difficulties contacting respondents over the phone. Successful contact is subject to mobile network availability and quality, whether the respondent’s mobile phone is charged and operational, whether the respondent answers a call from an unknown number, etc. After successful contact, nonresponse can equally result from refusal of the respondent to participate in the interview or a breakoff mid-way through the interview. These two sources of nonresponse are also present in F2F surveys but could be more substantial in phone surveys since respondents might be less responsive to an unseen interviewer over the phone than an interviewer they meet in person. _Bias_ due to this nonresponse will be introduced if the nonresponse is nonrandom with some segments of the population being more likely to not respond. Given the additional sources of nonresponse common to phone surveys, there is also a higher potential for systematic bias due to that nonresponse.

# <mark>2.1 Methods to Counteract Bias</mark>

While coverage and nonresponse bias are real concerns with phone surveys, there are methods to attempt to reduce the bias. The methods available will vary according to the type of frame used for the survey. There are three predominant types of frames used for telephone surveys: (1) existing representative F2F surveys that collected phone numbers of respondents (for example, LSMS-ISA, DHS, HBS, etc.), (2) a list of phone numbers from a telecom provider, and (3) a list of numbers generated randomly (random digit dialing, or RDD) (Himelein et al, 2020). While there are advantages 3