When psychologists and sociologists take a big-picture view of early childhood development, they almost always notice a correlation between income and child behavior. Specifically, children being raised in poverty tend to perform worse than higher-income children on language development, executive function, socio-emotional development, and even brain activity. These facts are based on correlational research (where both income and child outcomes are measured variables). What would happen if we could experimentally test the effect of extra income? We could then test whether extra income causes child outcomes to improve later on.  That’s the goal of a major study called Baby’s First Years (BFY). Here’s a summary of the project:

NBER (May 2025) posted new findings from the Baby’s First Years RCT, studying the effects of providing unconditional cash transfers to low-income, new mothers in the US. This high-quality RCT found no impacts on any of the study’s primary child development outcomes at the four-year follow-up.

And:

Developmental differences between children growing up in poverty and their higher-income peers are frequently reported. However, the extent to which such differences are caused by differences in family income is unclear. To study the causal role of income on children’s development, the Baby’s First Years randomized control trial provided families with monthly unconditional cash transfers. One thousand racially and ethnically diverse mothers with incomes below the U.S. federal poverty line were recruited from postpartum wards in 2018-19, and randomized to receive either $333/month or $20/month for the first several years of their children’s lives.  After the first four years of the intervention (n=891), we find no statistically significant impacts of the cash transfers on four preregistered primary outcomes (language, executive function, social-emotional problems, and high-frequency brain activity) nor on three secondary outcomes (visual processing/spatial perception, pre-literacy, maternal reports of developmental diagnoses).  Possible explanations for these results are discussed.

Questions

1. This was an experiment. What was the manipulated variable, and what were its levels?
2. Why did the researchers randomly assign families to the two conditions? What does this allow them to do? (Use the terms “third variable” or “internal validity” in your response)
3. There were four major dependent variables. What were they?
4. Sketch a bar graph of one of the results of the study.
5. Here’s the full report from the Baby’s First Years team. Scroll to Figure 2, on page 41, and study the interval plot you see there. What does one of the squares mean? What does the vertical dashed line indicate? What does one of the horizontal bars mean? All of these interval plots include the dashed line….what does this mean, and how is it related to the summary of the study?
6. Does this study support the claim that “providing low-income families with an extra $4000 per year causes their children have better developmental outcomes? Apply the three causal criteria of covariance, temporal precedence, and internal validity.
7. Chapter 11 concerns null effects. First, why does this study show a null effect? Second, I would argue that this study’s design helps us trust the null finding as “real” and not due to methodological weaknesses. Review the concepts in Table 11.3 and apply at least one of them to this study.

Here’s an important detail: An early set of data from the BFY study did show an improvement; specifically, at one year of age, babies in the extra cash group were showing improved brain activity (here’s a  description of that result). But in this 4-year follow-up, there was no difference between the two cash groups on brain activity.