On 26 Mar 2008 at 23:56, Jim Clark wrote: > > But no rational person would expect No Diathesis + No Stress to lead to a > disorder. > > So on what grounds is this potentially huge class of interactions deemed > irrelevant to Harris's thesis?
I'm happy to defer to Jim's superior knowledge of statistical design. In fact, as I've admitted, I'm finding this particular issue quite difficult going and I've been doing what I said I wasn't going to do, namely re- writing Judy Harris's work for her. I may well have misrepresented her views in the process. Jim should read her in the original (he says he hasn't) not as filtered through my imperfect attempt at a summary. But let me try yet again (I never learn, I guess). Her first point is that for most things, there are no demonstrated main effects of the home environment on children. So the developmentalists try to invoke gene- environment interaction as an alternative explanation. But since they can't point to main effects, they must produce a gene-environment interaction in which there is no main effect. She quotes Maccoby: "Nowadays, interactions between parenting styles and possible genetic attributes are a matter of active interest in developmental psychology...[One group of researchers] found that a given parenting style has a different effect on a child who is temperamentally bold and adventurous than it does on a timid, shy child...If we were to aggregate the two kinds of children together, some of the parenting effects would wash out" (Maccoby, 2002 quoted in No Two Alike, p. 56). In other words, in order to save their bacon (or sorry asses, take your pick), gene-environment supporters must come up with a kind of gene- environment interaction in which main effects average out to zero. To quote Harris (p. 57-58): "Can a gene-environment interaction explain how the net effect of environmental conditions can average out to zero or near zero? Yes, if it's the crossover kind of interaction". But she then says: "Crossover interactions, however, are rare in nature...the kind of interaction that is far more common in nature doesn't involve a crossover but only what might be called "sensitivity". She then says that the evidence that Maccoby reported was for sensitivity interactions. Now, here's where things get particularly dicey for me, understanding- wise. But I think what Harris argues is that Maccoby then cites sensitivity interaction examples in the few cases where there is evidence for main effects of home environment, namely, IQ, criminal behaviour, and mental illness. As there _is_ a home environment effect for these cases, these examples are irrelevant to the situation where you try to explain why there is no home environment effect because gene-environment crossover cancels out opposing influences of the home environment. Did I at last ace it? Do I get the high-five? Can I pump my arm in the air like Rafa Nadal, the King of Clay? I think I'll wait to celebrate. A few additional thoughts. Above, I give a quote in which Maccoby cites a crossover example. This example, used to explain zero overall main effect of parenting style on child temperament because the parenting has opposite effects on two types of child, is probably Jerome Kagan's. Harris discusses this research elsewhere in her book (p. 68) and shows that it has never been adequately presented in published form, concerns only young children, and is generally dubious and untrustworthy (my words). I also wonder about the list she provides of IQ, criminal behaviour, and mental illness as characteristics which are affected by family environment. I'm ok with criminal behaviour, and for mental illness she names schizophrenia, and suggests that a promising hypothesis is "that a virus infection may trigger the disorder in susceptible individuals" (which would be different from say, blaming the mother, as traditional snide psychological theory does). But for IQ, I wonder if she's thinking about the effect of the family environment only in the child. There's a strong age effect, and while there's some early effect of the shared environment on IQ, this falls to zero by the time the child is 12 years old (e.g. Bouchard, 2003). So I'd take IQ off the list if we're talking about adults. Stephen Bouchard, J., & McGue, M. (2003). Genetic and environmental influences on human psychological differences. Journal of neurobiology, 54, 4-45. [See Figure 7] ----------------------------------------------------------------- Stephen L. Black, Ph.D. Professor of Psychology, Emeritus Bishop's University e-mail: [EMAIL PROTECTED] 2600 College St. Sherbrooke QC J1M 1Z7 Canada Subscribe to discussion list (TIPS) for the teaching of psychology at http://flightline.highline.edu/sfrantz/tips/ ----------------------------------------------------------------------- --- To make changes to your subscription contact: Bill Southerly ([EMAIL PROTECTED])
