Does IQ differ depending on the family structure in which one grew up?

Note: This is a section of a longer article. To go to the start, click here.

Yes, and those that grew up in a nuclear family seem to have the highest IQ. In our battery, we had a question that asked our participants about the family structure in which they grew up with following seven response options:

• Nuclear family (e.g. lived with both biological parents)

• Single parent family

• Stepfamily (e.g. lived with one or more remarried parents)

• Extended family (e.g. lived with parents and grandparents)

• Grandparent family (e.g. raised by one or more grandparent)

• No family (e.g. orphanage)

• Other family structure

One important thing to note is that, as very few people in our sample choose one of the last three options, we discarded them from the analysis. Another thing to note is that, of the remaining options, nuclear family was chosen most often (n = 427), with single parent family (n = 91), stepfamily (n = 60) and extended family (n = 54) being chosen much less often. This means that the IQ score for these three groups were estimated with less precision, as indicated by larger confidence intervals in the figure below. Finally, before checking the differences in IQ between these different family structures, we have statically adjusted our IQ scores to be independent of the effects of gender, age and data source.

With these caveats, the largest IQ was estimated in participants that grew up in their nuclear families (mean IQ = 102), followed by those that grew up in single parent families (mean IQ = 98), stepfamily (mean IQ = 96) and extended family (mean IQ = 95). However, even though these mean IQ estimations differ, statistically speaking, nuclear family IQ significantly differed only from stepfamily and extended family IQ, but not from single parent family IQ. Importantly, these differences seem to be independent of a childhood class and wealth as they remained even after we statistically accounted for these factors. A figure below shows how the four family structures differ in IQ, together with confidence intervals around those IQ estimations.

What do the other studies say?

Although we did not find studies that specifically examined the differences in IQ between people growing up in different  family structures, there are studies that investigated different, but potentially related outcomes. For example, children in nuclear families generally show better health outcomes, fewer behavioral issues, and higher academic achievement compared to those in single-parent or blended families (e.g., Blackwell, 2010; Ginther & Pollak, 2004). Thus, it could be said that our findings did not contradict previous findings, further expanding prior results to include IQ. 

Takeaways

• IQ differs depending on the family structure in which a person grew up, being highest in those from nuclear families compared to other family types (extended family or stepfamily)

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