There is a major thread in the parenting literature that claims, in short, that parenting (short of outright abuse) has little to no effect on adult outcomes that we care about. Two exemplars in this category include The Nurture Assumption and Selfish Reasons to Have More Kids. This claim is largely based on twin and adoption studies, which allow us to attribute the observed variance in traits to genetic, shared environment, and non-shared environment factors. The general pattern is that lots of traits are about half genetic and half non-shared environment, with little contribution from shared environment. There is a major embedded assumption in this line of reasoning: that parenting effects are mainly in the shared environment. It turns out that this assumption is not a particularly good one.
A review article on research into the non-shared environment was released about two years ago, and it provides some fascinating data on this subject. I will quote some sections at length, but the entire paper is worth reading. Here is the first excerpt of interest:
For example, parental warmth and control have been assessed in hundreds of studies as the two ‘super-factors’ of parenting which are then correlated with children’s outcomes. These studies have traditionally assumed that parenting is a shared environmental factor in the sense that only one child per family was considered and parent–child associations were analyzed ‘between’ families. However, by studying more than one child per family and by targeting parenting that is specific to each child, it is possible to investigate the extent to which parents’ warmth and control differ for children ‘within’ families. Research of this kind has shown that parents do treat their children differently. If you ask parents about their differential parenting they report only modest differential parenting (sibling correlations of ~0.70) but if you ask children about it you might think they were raised in different families (sibling correlations of ~0.25). Observations of parent–child interactions support not the parents’ but the children’s view (sibling correlations of ~0.20).
In short, parents think they treat their kids the same… but the kids think the parents treat them differently, and outside observations would support this claim. If anything, the outside observer sees slightly more unequal treatment than the kids themselves do. This indicates that the vast majority of parenting effects would show up in the non-shared environment.
That said, modern study designs have indeed allowed us to decompose the known sources of non-shared environmental influences. Here is the relevant data from the paper:
The proportion of total variance accounted for in outcomes such as adjustment, personality and cognition was 0.01 for family constellation, 0.02 for differential parental behaviour, 0.02 for differential sibling interaction and 0.05 for differential peer or teacher interaction. Moreover, these effects are largely independent and they add up to account for 13% of the total variance. If non-shared environment accounts for ~40% of the variance in these domains, we could say the cup is already more than one quarter full.
The most important takeaway here is that we really don’t know where most of this variation comes from yet, and it’s likely that some of the remainder is still unobserved parenting/family/peer/teacher effects. Of the one-third that we can explain, it seems like about 20% of that effect is directly from parenting, a full half of that effect is from inside-family dynamics, and the remainder is peer and teacher effects. These statistics of course come from a large number of people from the general public, and it’s not clear how much we can generalize from this. Do parents have any effect on how siblings treat each other, for instance? What happens if the child is homeschooled? Do parents influence the kids’ choice of peers? This seems like a lower bound on what is possible from parenting techniques, in my opinion.
I will also note that I’m relatively optimistic that genetics play such a strong role – I picked Divia for good reasons. Insofar as we are largely an expression of our genes, these genes have led to good results. A child that is mostly the average of the two of us would be someone I very much want to exist.
This does, of course, leave quite a lot of variance unexplained. The author actually concludes by saying:
The message is not that family experiences are unimportant but rather that the relevant experiences are specific to each child in the family, not general to all children in the family. However, my main conclusion has to be that the key question largely remains unanswered: why are children in the same family so different?
This non-shared environment factor by construction includes basically everything that happens in life. That means all of the random perturbations that happen over a lifetime might account for much of this variance:
It is also possible that non-systematic factors, such as accidents and illnesses and other idiosyncratic experiences, initiate differences between siblings. Compounded over time, small chance differences in experience might lead to large differences in outcome, as discussed in the next section. The 1987 paper concluded that ‘one gloomy prospect is that the salient environment might be unsystematic, idiosyncratic, or serendipitous events such as accidents, illnesses and other traumas, as biographies often attest’. It is striking how often biographies and autobiographies point to chance as a tipping point to explain why siblings are so different. Illnesses and accidents also feature in interviews with parents of discordant identical twins in explaining why they thought their children differed. Support for chance as a source of non-shared environmental influence comes from quantitative genetic research that suggests that non-shared environmental effects are trait specific and age specific. That is, non-shared environmental effects on one trait are largely uncorrelated with such effects on other traits and non-shared environmental effects at one age are largely uncorrelated with such effects at other ages.
Clearly the role of random chance and idiosyncratic events plays a large role in our narrative of these individual differences. The statistical evidence, that the non-shared environmental factors are largely uncorrelated with one another, is an interesting finding. This doesn’t necessarily mean it’s entirely random chance, it means that any intervention we do is unlikely to fully generalize. Depending on your perspective, this could be a good or a bad thing. It does suggest that everything we does has lots of little, cumulative effects. There may be a lot of independent factors to get right, each of which has a small but positive impact on our kids’ lives. But looking on the bright side, that also means that if you screw one or two things up, you still get another chance, and the net result can turn out quite good.
I definitely wonder how much research like this affects people’s willingness to invest more effort in their children. I am already quite motivated to provide Lydia with a good life, as I best understand it. It seems to me like my interactions with her at the very least impact her experience right now, which is something I definitely care about. Intuitively, it seems crazy to me that we might not have a major impact on our kids. Reading this paper does make me think that the research is more in line with my beliefs than I felt like was portrayed in the aforementioned literature. I don’t believe that parents are the only effect on a child’s life by any means, but it certainly seemed like one in mine, and from working with many people it seems to be quite important. Realizing that parents do treat their kids differently, and that this produces different results, along with the combination of a huge number of individual life events, is my main takeaway from this paper. We can’t completely determine the lives of our children – and maybe we shouldn’t be able to do so – but we clearly have an impact, and I want that impact to be as positive as possible.
Leave a Reply