proximity of neighborhoods and the population density made it highly unlikely that control neighborhoods would not eventually find out about the intervention. We pay close attention to spillovers in our analysis. A map of the intervention area and the selected neighborhoods in Phase 1 and Phase 2 of the larger infrastructure project, PROGEP, is provided in Figure 1. The full time-line of the project is described in Figure 2.

Finally, we note that PROGEP was rolled-out in two phases.<sup>19</sup> PROGEP’s infrastructure component (rehabilitation of old water basins, implementation of new drainage pipelines, etc.) was implemented in Phase 1 areas between 2014 and 2016 and in Phase 2 areas between 2017 and 2019. Given that the former benefitted from improved drainage infrastructure before the latter, we might expect to see differences in the effect of the OQP intervention in each Phase. This is something we take into account in our empirical analysis.

# **5. Data collection and empirical approach**

# _Data collection_

Data were collected at the individual, household and CBO levels. In each neighborhood, 15 households were randomly chosen to be surveyed, giving a total sample size at baseline of 2,400 households. The household questionnaire collected information on household demographics, livelihoods and income sources, socioeconomic characteristics, health outcomes, exposure to flooding, knowledge of risk mitigation methods, and attitudes towards community participation and one’s general responsibilities vis-à-vis the community (and viceversa). Within each household, data relating to certain variables (education, health, etc.) were collected for all individual household members, with a total sample size of 28,010 A CBO-level questionnaire was also administered as a group survey. This survey focused on basic group characteristics, their motivations for participating, their attitudes towards civic participation, and the nature of CBO activities. The end-line survey differed slightly for treatment and control CBOs as it aimed to collect data to allow us to gauge the awareness of control CBOs about OQP and whether or not this had influenced their activities, in order for us to construct a measure of potential spillovers.

The baseline survey was carried out in July 2015.<sup>20</sup> The end-line survey was carried out during November 2016. The attrition rate was low. Out of the 2,400 households surveyed at baseline, only 115 could not be included in the end-line survey (an attrition rate of less than 5%).

# _Baseline characteristics_

Table 4 presents the average values for a range of baseline household characteristics for the treatment group and the control group, along with the difference between groups and the p- value of a t-test of whether this difference is statistically significant at conventional levels (pvalue < 0.10; this is identifiable by the presence of one or more stars next to the p-value).

The first set of variables relates to the characteristics of the household head. Approximately 70% of household heads are male and the vast majority (96%) are Muslim. Most are married

> 19 Phase 1 covers Dalifort-Thiouorour (communes of Wakhinane Nimzatt, Djeddah Thiaroye Kao, DalifortFoirail, Hann Bel Air and the Western halves of Yeumbeul Nord and Yeumbeul Sud) and Phase 2 covers Yeumbeul-Mbeubeuss (Keur Massar, Malika and the Eastern halves of Yeumbeul Nord and Yeumbeul Sud). 20 The baseline survey took place before neighborhoods were assigned to the treatment and control groups, to avoid any anticipation effects from CBOs and households.

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