_3_ ( _4_ ) iirr iirr VV = αα+ ββ ZZ + εε Where _Vi,r_ is again a dummy for whether respondent i selected by method r is vaccinated. The subscript _r_ denotes whether _V_ was obtained by interviewing a purposively selected respondent vs. a randomly selected respondent (equation 2); whether _V_ was obtained from the purposively selected respondent vs. as part of eliciting the (proxy-reported) vaccination status of all household members aged 15 and above (equation 3)<sup>9</sup> ; or whether _V_ was obtained through random selection of a respondent vs. from the proxy reported vaccination status of all individuals in the household aged 15+ (equation 4). Our estimates of interest are _β1_ , _β2_ , and _β3_ , the coefficients on _Di,r_ , _Ti,r,_ and _Zi,r_ , respectively, which are dummies for whether observation _i,r_ is part of the randomly selected sample of respondents as opposed to the purposively selected sample ( _Di,r_ in equation 2); part of the sample for which a proxy reported vaccination status was collected as opposed to the sample of purposively selected respondents ( _Ti,r_ in equation 3); or part of the randomly selected sample as opposed to the proxy-reported sample ( _Zi,r_ in equation 4); . If our predictions are confirmed, _β1_ and _β2_ should be significant and negative. Additionally, we would expect _β3_ to be insignificant as the randomly selected respondent is sampled from the list of all household members aged 15 or older. To facilitate comparisons with the administrative data (without the need for assumptions regarding non-coverage of children), we additionally use the proxy reported vaccination status of all household members (i.e. not just those aged 15+) to estimate general population vaccine coverage.

# 3.2 Measurement errors

## <u>Hypothesis 3: Survey mode effects</u>

Our third hypothesis relates to differences in survey modes. Concretely, it is conceivable that interviews conducted over the phone lead to different estimates than interviews conducted inperson. For example, respondents may be less inclined to answer truthfully when surveyed by an enumerator over the phone, pay less attention to the questions asked, and enumerators cannot ascertain the circumstances under which the interview takes place (e.g., other people present in the room, respondents getting distracted, etc.). This may lead to different reported vaccination rates in phone surveys than in in-person surveys. It is not obvious ex-ante whether phone or in-person surveys would find higher vaccination rates. However, for mode effects to explain (part of) the observed misalignment between surveys and administrative records, phone surveys would have to induce more respondents to report to be vaccinated. Our third hypothesis thus states the following.

**Hypothesis 3:** Asking respondents for their vaccination status over the phone as opposed to in person leads to greater reported vaccination rates.

To test this hypothesis, we again rely on the vaccination survey administered in person as part of the ESS 5 in Ethiopia. An ideal setup to test this hypothesis directly would be to randomly assign respondents either to the in-person survey or to the phone survey and conduct interviews around the same time. We do not have this kind of setup: we interview the same respondents both in

> 9 This includes the purposively selected respondent’s vaccination status which is a self- rather than a proxy-report.

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