Here is a parenting website (Dr. Laura… how many Dr. Laura’s are there out there?), it attempts to refute Bryan Caplan’s parenting advice in Selfish Reasons to have more Kids. She’s a bit condescending, which makes me feel better when I point out that she doesn’t seem to understand the nature/nurture problem that twin (and adoption) studies try to solve.
Now, a research team at the University of Washington in Seattle has found that four year olds who watched 3.5 hours of TV per day were 25% more likely to exhibit cruelty and meanness to others (as reported by their mothers) between ages 6 and 11 than those who watched none. That's a far-reaching, big effect.
Were half the kids randomly assigned to watch 3.5 more hours a day? Or could we just as well say that parents who let their kids watch more television (and pass on genes that influence children to want to watch more television), also pass on genes that positively correlate with violent behavior?
while previous studies have linked television to aggressive behavior in older children and adolescents, this is the first time the association has been firmly established for four-year-olds…
Zimmerman's team also found that children whose parents regularly exposed them to ideas by reading aloud, eating meals together, or taking them to museums, for example, were a third less likely to become bullies.
Nobody doubts links and associations, the question is whether they are linked causally or by a confounding variable – genetics. The research being cited doesn’t solve that problem. It doesn’t even try to, and the researchers who are giving parenting advice based on it should know better.
Lets state clearly what I think she and other people miss -- whether nature or nurture is effecting children is not observable phenomenon in normal children. Any time there is a positive correlation between parenting and long term differences, we don’t know whether the parenting caused it or if genetics caused both. Good thing there are two special kinds of families, twin and adoption families.
Twin studies looks at two kinds of twins (fraternal and identical), measures if how much difference in life outcomes there are between them. Since identical twins share 100% of their genes, and fraternal twins only share 50%, we can see how much genetics matter by measuring how much more alike identical twins end up being than fraternal twins. The answer: identical twins are a lot more alike.
Adoption studies are easier to understand for some people. They notice that children end up a lot more like their genetic parents than the parents who raised them.
I did get one good thing from her post, a link to this paper criticizing twin research. It’s locked, so I’ve only read the abstract. But it calls into question the equal environment assumption. I would like to know how. I don’t suspect fraternal and identical twin sets are raised in radically different ways.
Here is Bryan Caplan on Econtalk discussion Selfish Reasons to have more Kids.
