to be the subject of a full listing operation, which could then serve as a sampling frame.<sup>6</sup> Finally, in all three countries, as in other developing countries, forcibly displaced populations are excluded from the available national census and sampling frames. Hence, we used UNHCR data on registered Syrian refugees, which had to be combined with host population estimates, typically at the sub-district level. For more details on the sampling strategy, please refer to (Aguilera, et al., 2019).

The sample was stratified into groups of interest, depending on the country context. In Lebanon, the survey is representative of the host community and the Syrian refugee population. In Kurdistan, the scope of the survey was expanded to include internally displaced persons (IDPs), so that the survey is representative of the host community, of Syrian refugees in camps and outside camps, and of IDPs in camps and outside camps. In Jordan, the original design could not be implemented because we could not access the new sample frame based on the 2015 Jordanian census. The design was then amended to include a representative sample of the Za’atari and Azraq camps (which account for the vast majority of the Syrian refugee camp population in Jordan). It was complemented by purposive samples of the surrounding governorates, Mafraq and Zarqa (where the sample included areas physically proximate to the camp, and other areas of high Syrian refugee prevalence). In the Amman governorate, a purposive sample was drawn, combining a geographically distributed sample with a sample of high prevalence Syrian refugee areas as indicated by the Jordanian Department of Statistics. In what follows, _Jordan sample_ refers to the households surveyed in Za’atari and Azraq camps, areas surrounding the camps in Mafraq and Zarqaa governorates, and Amman governorate, except in regression analysis, where we only use the Amman sample.

The survey instrument was administered across Lebanon, Jordan, and KRI, with slight modifications depending on the structure of refugee living conditions. The survey includes detailed questions on demographics, employment, access to public services, health, migration, and perceptions. The results offer comparisons between a) the refugees before and after displacement, b) host communities before and after the influx, and c) the host communities and the displaced. These comparisons enable us to ascertain past and current outcomes to benchmark the host communities prior to the influx, determine whether the displaced differ systematically from the broader population of origin, identify the immediate effect of displacement on the forcibly displaced, and explore how the local influx of the forcibly displaced has shaped host community outcomes.

There are several empirical challenges in assessing the impact of a population influx on the host populations. Although they can potentially be addressed if appropriate data are available, they cannot be addressed with a single survey, however carefully designed. In the (empirically) ideal setting, which rarely materializes, the forcibly displaced population is distributed randomly across the host country or distributed in a manner that is exogenous to any outcomes of interest. In this setting, before-after comparisons of host community outcomes yield valid causal estimates of the impact of the influx. In practice, the forcibly displaced either self-select into areas based on observable and unobservable characteristics or are located in certain areas as a result of host government policy. In this context, it becomes important to account for pre-existing trends in local characteristics that could in themselves explain the observed outcomes. In the absence of such data, one would conflate the effect of the influx with the influence of these trends.

> 6 The finest level of disaggregation available was at the level of the _Circonscriptions Foncières (CF)_ , which were generally too large to be listed (as some have populations of over 100,000).

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