Assessment of heterogeneous Head Start treatment effects on cognitive and social-emotional outcomes

Current Understanding of the Roles of Gut-Brain Axis in the Cognitive Deficits Caused by Perinatal Stress Exposure

The term 'perinatal environment' refers to the period surrounding birth, which plays a crucial role in brain development. It has been suggested that dynamic communication between the neuro-immune system and gut microbiota is essential in maintaining adequate brain function. This interaction depends on the mother's status during pregnancy and/or the newborn environment. Here, we show experimental and clinical evidence that indicates that the perinatal period is a critical window in which stress-induced immune activation and altered microbiota compositions produce lasting behavioral consequences, although a clear causative relationship has not yet been established. In addition, we discuss potential early treatments for preventing the deleterious effect of perinatal stress exposure. In this sense, early environmental enrichment exposure (including exercise) and melatonin use in the perinatal period could be valuable in improving the negative consequences of early adversities. The evidence presented in this review encourages the realization of studies investigating the beneficial role of melatonin administration and environmental enrichment exposure in mitigating cognitive alteration in offspring under perinatal stress exposure. On the other hand, direct evidence of microbiota restoration as the main mechanism behind the beneficial effects of this treatment has not been fully demonstrated and should be explored in future studies.

Assessment of the predictive power of a causal variable: An application to the Head Start impact study

In a study attempting to estimate a causal effect of a causal variable, an assessment of the predictive power of the causal variable can shed light on the heterogeneity around its average effect. Using data from the Head Start Impact Study, a randomized controlled trial of the Head Start, a nation-wide early childhood education program in the United States, we provide a parallel comparison between measures of average effect and predictive power of the Head Start on five cognitive outcomes. We observed that one year of the Head Start increased scores for all five outcomes, with effect sizes ranging from 0.12 to 0.19 standard deviations. Percent variation explained by the Head Start ranged from 0.56 to 1.62%. For binary versions of the outcomes, the overall pattern remained; the Head Start on average improved the outcomes by meaningful magnitudes. In contrast, in a fully adjusted model, the Head Start only improved area under the curve (AUC) by less than 1% and its influence on the variance of predicted probabilities was negligible. The Head-Start-only model only achieved AUC ranging from 50.22 to 55.24%. Negligible predictive power despite the significant average effect suggests that the heterogeneity in effects may be large. The average effect estimates may not generalize well to different populations or different Head Start program settings. Assessment of the predictive power of a causal variable in randomized data should be a routine practice as it can provide helpful information on the causal effect and especially its heterogeneity.

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The average effect and predictive power of Head Start were assessed.

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Head Start increased scores for five cognitive outcomes with effect sizes ranging from 0.12 to 0.19 standard deviations.

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Head Start only explained less than 2% of the child-level variance in cognitive outcomes.

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Head Start only achieved about 50% in AUC and improved less than 1% in AUC when added to a full model.

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The impact of Head Start is meaningfully sized on average but the effect heterogeneity is large.

Distributional effects on children's cognitive and social-emotional outcomes in the Head Start Impact Study: A quantile regression approach

Heterogeneity in treatment effects of the Head Start, a federally funded early childhood development program in the United States, has previously been found in the Head Start Impact Study (HSIS), a nationally representative randomized controlled trial. While individual characteristics have been extensively examined as sources of effect heterogeneity, treatment effects may vary as a function of outcome distribution (i.e., distributional effect). Using quantile regressions, we investigated distributional effects of the Head Start on eight child developmental outcomes for first year, second year, third year, and the 3rd grade year follow-up in the HSIS data. For PPVT and Applied Problems, the effects varied substantially across quantiles in the first follow-up, but they were positive overall. The effects at the lower quantiles were larger and were sustained beyond the first follow-up (PPVT [95% CI] at 10th and 90th quantiles: 8.74 [6.22, 11.27], 3.32 [0.82, 5.81]) in the first follow-up and 5.72 [2.66, 8.77], −1.66 [-3.69, 0.37] in the second follow-up). For Behavior Problems, the effects were only positive for the lower quantiles in the first follow-up, but they became null in the latter follow-ups. For Letter-Word Identification, Spelling, and Pre-Academic, the effects were positive in the first follow-up with moderate variation across quantiles. In the second follow-up, only the effects at the lower quantiles were statistically significant, although they faded in the latter follow-ups. For Oral Comprehension and Social Skills, effects were null for all follow-ups. The Head Start had meaningful distributional effects for a range of child developmental outcomes, and distributional effects should be routinely assessed for better understanding of child developmental programs.

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The Head Start effects on children’s cognitive and social-emotional outcomes were estimated using quantile regressions.

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The Head Start effects were more beneficial at the worse-performing part of the outcome distribution.

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A substantial variation in treatment effects was found along the outcome distribution.