Apples, Oranges, and Lesbians: The Nurture Assumption Just Will Not Die
The finding of this study seems straightforward – indeed, I was able to say it in a sentence. However, the conclusions we are able to draw from these finding are anything but.
The study looked at sample of 20% of the individuals in the 2006 Canadian census. Unlike previous studies, it has the strength of being able to examine a large, truly random sample.
Previous studies into the matter have claimed to find no significant differences between the children of gay and parents vs. those of straight parents. However, those studies apparently suffered from serious methodological weaknesses. The author of the current study explains:
Generally speaking the literature is characterized by several different types of data bias and small samples that lack any power … Although a proper probability sample is a necessary condition for making any claim about an unknown population, within the same-sex parenting literature researchers have studied only those community members who are convenient to study … Of the fifty-three studies reviewed here, only seven used probability samples. All of the other studies arrived at their samples through means that introduced various levels of bias. Some studies recruited individuals from sperm bank data sources or other types of reproduction technology providers. Other studies used Internet surveys where the respondents were recruited by various methods: parent forums, gay and lesbian web-sites, and online advocacy organizations. Many studies recruited through LGBT events, bookstore and newspaper advertisements, word of mouth, networking, and youth groups. A common method of recruitment was to use a combination of the above methods to form a sample base, and then recruit friends of the base. Still other studies failed to even mention how their samples were arrived at. Each different procedure has a different and unknown source of bias.
Aside from the problem of non-random samples, most of the existing parenting studies contain tiny sample sizes. Of the fifty-three studies examined here, only two had sample sizes larger than 500. Much more common were sample sizes between 30-60. The problem with such small sample sizes is that the data cannot generate any power for statistical testing, and low power means there is a small chance of rejecting a false null hypothesis. Hence, the very small sample sizes found in many of these studies creates a bias towards accepting a null hypothesis of ‘‘no effect’’ in child outcomes between same-and opposite-sex households.
OK, so this study “corrects” for these shortcomings by relying on a large, random sample. Still, the rarity of same-sex couples meant that there were few in the sample. Indeed, there are apparently only 423 gay and 969 lesbian families in the entire nation of Canada. Nonetheless, its sample is larger than most such studies.
The study found that children with lesbian “parents” were only 60% as likely to graduate from high school (sons 76%, daughters 45%), while children with gay male “parents” were only 69% as likely (daughters 15%, sons 161%). The disparity remained significant even when certain controls were introduced (such as parental education).
So case closed, right? We can now safely conclude that two opposite-sex parents are important for children’s development, yes? Of course not, not even close.
First of all, despite this study’s improvements over its antecedents, it suffers from a fundamental weakness. It is in essence a classic family study, one that looked at associations within families and then emboldens others to draw conclusions (as illustrated by the title “A Married Mom and Dad Really Do Matter: New Evidence from Canada”) about “family constellation variables.” Yup, there’s your problem: classic confusion of correlation with causation.
You can’t make causal determinations from standard family studies. Even with heterosexual parents, finding associations between parents and their biological children tells you nothing about whether anything about the parents’ rearing of the children had anything to do with what you find, not for the least reason being heredity. Just as finding that substance abusing parents have children that go on to do the same, heredity confounds you at every turn. This is because, as readers should know by now, all human behavioral traits are heritable.
Hence, a key problem is that comparing gay/lesbian parents to straight parents – even when you put in your “controls” – is essentially comparing apples to oranges. I don’t have to tell you that gays and lesbians – particularly the ones that try to live in married/civil union couples are systematically different from straight individuals. A passage from the study illustrates this point:
in the context of gay parenting … avenues through which these households are formed are many and complicated. As noted by Stacey and Biblarz … these families often have experienced a prior divorce, previous heterosexual marriages, intentional pregnancies, co-parenting, donor insemination, adoption, and surragacy.
The biological children of gay and lesbians can hardly considered to be genetically comparable to those of straight individuals, even discounting the sexual orientation itself.
That’s if they’re even their biological children. Here’s another finding of the study:
There are a higher number of visible minority children for gay households (28 % compared to 13 % for common law couples), and a higher number of disabled children (13 % compared to 6 % for opposite sex married parents). This may imply a high number of adopted children in gay households, but interestingly there are no cases of inter-racial same-sex families within the 20 % sample.
I don’t even need to touch the higher fraction of “visible minority” and disabled children in the same-sex parent sample. That’s just icing on the cake at this point.
Having same-sex parents, in and of itself, likely has no impact on children’s development. It would be really strange that if it did, since parenting in general (across the broad range that constitutes “normal” parenting) has no impact on how children turn out. That was the revelation in my first blog post, and it’s a fact that remains underappreciated to this day. This study of gay parents doesn’t change our understanding.
The failure to recognize the broad null effect of nurture (“The Nurture Assumption”) is pervasive even in the HBD community, the people who should of all know better.
Indeed, a recent blog post reciting some quips from Robert Plomin (a foremost behavioral geneticist) rekindled a discredited idea to explain the consistent non-effect of the shared environment term (the fact that there is no correlation between children raised together once you take genes into account) (emphasis in original):
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.
Parent-child interaction was the Occam’s Butterknife way for developmental psychologists to rescue parenting after studies failed to turn up evidence for its effects. Judith Rich Harris and Steven Pinker both long since dispatched this idea, as I explained:
It requires that there are no across the board differences from one set of parents to another. To see why, imagine parents did have some effect. Even if there were differences in the exact treatment each child received, there are going to be systematic similarities with the way each set of parents treat all their children. If such an effect existed, it would turn up in the shared environment, since kids growing up together would be impacted by these across the board similarities. But the shared environment influence is in fact negligible.
It requires perfect crossover interaction. Let’s say you assume that parental effects – whatever their across the board similarity for a given set of parents – had totally idiosyncratic effects on children. Then in order to explain the null effect of the shared environment, the sum of these effects on children’s traits had to be exactly zero. Any number of children exhibiting one sort of effect would have to be balanced by an equal number of children exhibiting the exact opposite effect. That is a rather large stretch.
Occam’s razor and….
The notion that parental influences exist, but the factors that vary among parents in how they treat their children across the board must either have no consistent effect or must perfectly cancel across children such that it gives the appearance in the data that it has no effect at all requires us to entertain many more causal entities that the simpler idea that they just have no effect at all.
Of course, it gets worse for parenting, thanks to studies into the effects of birth order:
In any case, there is additional trouble for the idea of significant parental impact: it has to contend with the absence of birth order effects. Thorough analysis has failed to find any systematic differences in children due to birth order. Birth order is one case of systematic, non-genetic differences in the home environment of children. It’s hard to reconcile the existence of parental effects with the failure to find anything when looking at a reliable systematic difference in the parental environment.
Parenting is simply less important than most people think. But as with the issue with health and obesity, even individuals who understand the pervasiveness of nature and the apparent stochasticity of what we call “environment” like to believe there is some way they can exert control (see locus of control, courtesy Richard Harper).
To be fair to parenting, over at my comment at the blog I left the current unknowns about parenting:
Now, to be completely fair to parenting, some commenters on the matter, such as Steve Sailer, posit that parental effects are largely unimportant when looking at higher-SES, Western parents. The difference from one set of middle-class Western parents to another set may not matter much, but the difference might matter if we compared White Western parents to say poorer Latin American parents. On that we have to say the data don’t yet rule such a difference out. My own suspicion is that even in those cases, we will find that the difference – if any – stems from environmental impacts that only act in a negative way; e.g., we know that childhood malnourishment can stunt IQ, but nutrition beyond what’s adequate won’t raise IQ. In the same way, children from poorer families might miss out on critical developmental inputs. As well, they may miss out on key opportunities to achieve, which itself is perhaps more a function of the outside the home environment in which these poor children happen to dwell.
Only further research with non-Western, non-White samples can hope to answer this question. In either case, for now, the message is clear, parenting matters a lot less than society merits it, be those parents married, unmarried, straight, gay or lesbian.
As for the song for this post, while this song doesn’t have much to do with the subject, for some reason, it seems to me to fit: