test this idea by augmenting equation (1) to include interactions between treatment and proxies for alternative sources of information. Public certification effects on employment are 2.7 percentage points smaller for candidates with post-secondary education (standard error 2.8 p.p.) and 4.3 percentage points smaller for candidates with prior work experience (standard error 3.2 p.p.) (Table D.9, panel B). We also estimate the latent probability of being employed at endline as a single summary measure.<sup>26</sup> Candidates with above-median latent probabilities of employment have 6.9 percentage point smaller public certification effects than candidates with below-median latent probabilities (standard error 2.8 p.p.). These results show that certification can substitute for traditional sources of information about workseekers’ skills.<sup>27</sup> This is consistent with evidence that educational qualifications are more useful for members of groups facing statistical discrimination (Arcidiacono et al., 2010).

# **5.4 Skill at Scales**

We show that skill certification at a relatively small scale increases employment and earnings for certified workseekers. In this section we discuss conditions under which effects may vary with the scale of skill<sup>28</sup> First, employment and earnings effects may depend on scale if certified workseekers displace non-certified workseekers. It is unlikely that our experimental results are due to displacement of non-certified workseekers _in the control group_ . We certify only 2,247 workseekers in a metropolitan area with roughly 8 million people and 2 million employed workers (Statistics South Africa, 2016). The probability of certified and control group workseekers applying for the same jobs by chance is very small, and Harambee does not encourage recently-assessed workseekers to apply to specific jobs or search for work in specific areas.

It is possible that certified workseekers displace non-certified workseekers who are not part of the experimental sample. We cannot directly test for this, but we can evaluate the mechanisms that might generate it. Displacement is less likely if certification improves match quality and hence increases the share of latent vacancies that are worth filling, as in our conceptual framework and general equilibrium models of information frictions (Donovan et al., 2018; Jovanovic, 1979; 26We estimate the latent probabilities following Abadie et al. (2018). We regress endline employment on baseline demographics, education, assessment results, beliefs about assessment results, employment, earnings, and search behavior in the control group. We use the predicted values from these regressions in all treatment groups as latent probabilities for employment, adjusting the predicted values in the control group using leave-one-out estimation to avoid overfitting.

> 27This result is not explained by a correlation between workseekers’ skills and their education and past employment. We regress employment on treatment assignments, a single index measure of skill from Section 5.2, a measure of information about workseekers’ skills from this section, and a full set of interactions. The interactions between public certification and the single index skill measure remain close to zero, while the interactions between public certification and the measure of information about workseekers’ skills remain negative.

> 28There are few existing papers that study how the effects of specific active labor market policies change with scale. For job search assistance policies specifically, Crépon et al. (2013) and Lise et al. (2004) find larger-scale policies generate negative spillovers on non-participants, while Blundell et al. (2004) find no spillovers on non-participants.

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