Overall, the 26 causal studies examined 20 different measures of child development. To reduce multiple dimensions of this body of evidence, we combined them into 6 main outcomes: schooling, cognitive, behavioral and 3 types of health measures. Schooling outcomes included years of schooling, current enrollment, grade attaintment and high school grades. Cognitive outcomes included test scores from a range of psycometrically validated exams. Behavioral outcomes are largely comprised of self-reported risky beahviors for adolescents and parent-reported standardized indexes for behavioral problems for younger children. We grouped health outcomes into three categories: (1) height outcomes, which capture long-term nutrition, (2) weight outcomes, which consider short-term nutrition and physical activity,<sup>1</sup> and (3) other health measures, most of which were indicators of medical concerns such as lung capacity, hemoglobin levels, asthma episodes, ear infections and overnight hospitalization.

Several studies examined more than one group of outcomes. To facilitate the discussion of results, we refer to separate groups of outcomes within a study as a substudy. A study can have one substudy or multilple substudies. Twenty-six causal studies yielded 40 substudies with evidence on 6 outcomes (height, weight, health, schooling, behavior and cognition).

For each substudy, we categorized whether it detected null, positive or negative impacts of maternal work on child development for each group of outcomes it examined. If at least one outcome in a group is negative/positive in a statistically significant way, while impacts on other outcomes in that group are not statistically significant, we count it as evidence of negative/positive impact for the substudy.<sup>2</sup> If there was no statistically significant impact on any outcomes in the group, we count it as evidence of null effect. There were no papers which detected a statistically significant positive impact on one outcome in a group, and negative on a different one.

# Main findings: Impacts on children’s development

The most abundant evidence is on weight-related outcomes, followed by cognitive and behavioral outcomes (12, 8 and 7 substudies, respectively). The evidence is more scant on schooling, health and height outcomes, with 5, 4 and 4 substudies, respectively.

The majority of causal evidence from 10 countries over the last 20 years suggests that maternal work does not hurt children’s development. Of the substudies, 68% (27 out of 40) do not find evidence of negative impact, with 6 finding positive, and 21 null effects (Figure 1).

An interesting feature of the studies reviewed is that many of them use a wide range of outcomes, and only 2 corrected for multiple hypotheses testing, or adjusted for the probability of discovering a non-null effect purely by chance. While common practice in medicine, correction for multiple hypotheses testing started making forays into social science only recently.<sup>3</sup> Thus the 20-year span of our analysis incorporates many papers that were not yet submitted to this additional check.

> 1 Weight outcomes include deviations from the norm in both directions: underweight as well as obesity.

> 2 For example, the s t udy in Indonesia examines 2 indicators for health: hemoglogin and lung capaicty. The authors find statistically signficant impacts on hemoglobin, but not on lung capacity. We categorize this result as evidence of positive impact on health.

> 3 Some of the earliest papers that raised the question of correcting for multiple hypotheses testing and demonstrating sensitivity of results include Anderson (2008), List, Shaikh and Xu (2019), Kling, Liebman and Katz (2007).

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