## **2.4 Costs of CPS and other preschools**

Our cost estimates are based on the ingredient method<sup>11</sup> which aims to cost every resource required to make an intervention happen.<sup>12</sup> This includes construction costs as well as support costs, such as management, administrative and overhead costs. Total annual costs for running 500 CPS is estimated to be $3,136,743 for an average cost per school of $6,273 or $256 per child, which compares to roughly 22% of the GDP per capita ($1,160 in 2015). The estimated annual SPS costs are much higher at $12,602 per school and $426 per child.<sup>13</sup> Due to the lack of uniform quality standards no cost estimates for IPS were calculated. However, we anticipate the cost of IPS to be vastly lower. We obtain a back-of-the-envelop cost estimate of the IPS by using the CPS cost analysis from which we subtract all costs related to the construction (3%), the material (25%), the equipment (4%).<sup>14</sup> Based on this approach, the cost of IPS is estimated to be 68% of that for CPS i.e. $174.

# **3 Evaluation Design and Data**

## **3.1 Randomization and sampling**

This evaluation of the CPS program is based on a randomized controlled trial. All sample villages are situated in the south and northeast parts of Cambodia. Eligibility criteria for villages to participate in the study were: expressed demand for a CPS, a high poverty rate, and a large number of children aged zero to five years.

The study sample is composed of 305 villages. Before baseline, villages were randomly assigned to the control group or one of the three treatment groups: CPS (T1); CPS and D2D (T2); or CPS, D2D, and HBP (T3). Randomization was stratified to obtain a sample for which treatment is balanced within each of the 13 provinces of our sample.<sup>15</sup> The design is summarized in Table 1.

> 11 Therefore, our cost measures are not directly comparable to studies that base their costeffectiveness analyses on programmatic costs only (e.g. Brinkman et al. (2017))

> 12A full discussion of cost estimates can be found in the SIEF impact evaluation report (Berkes et al., 2019).

> 13The cost estimates reported here are based on a model using mid-range estimates for unobserved costs. Under all models, costs per child at SPS were 50%—126% higher than at CPS.

> 14This is probably an overestimation of the IPS cost since IPS cater to more students and the training costs were higher for CPS than they were for IPS.

> 15The randomization was performed with a list of 310 eligible villages provided by the government. Of these, 60 were assigned to the control group, 123 to T1, 63 to T2, and 64 to T3. Unfortunately, the randomization list contained erroneous village names and five of them were duplicated or could not be identified after the randomization even after substantial effort by MoEYS and the data collection firm. Therefore, the total number of villages decreased to 305. We treated this dropout as random and did not replace the villages. The randomization list also contained villages for which a CPS teacher was no longer available or for which no land could be secured for CPS construction. Therefore, only 91% of treatment group villages received a CPS. Since these factors are potentially endogenous, we do not treat these as random. To maintain ex-ante expected balance between control and treatment villages, these villages were therefore not removed from our sample.

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