i doubt if a study like that is even possible given the number of variables
It's a correlational study, which can infer that variable A predicts variable B. There can still be a large number of confounding variables present; as long as they change with the variables of interest, the study will still have reliability and validity (though poor internal validity). It's not far fetched that spanking predicts lower IQ. However, the act of spanking itself may not
cause lower IQ. There are probably a number of confounding variables that explain it. For example, it may be possible that parents from a lower socio-economic class are more likely to to spank their children. Children from a lower socio-economic class usually do not have the same access to high quality education that more priviledged children do. From another perspective, children from a lower socio-economic class may not have as quality of diets as higher class children; therefore, lower-class children's brain development and nerve plasticity may be more hindered when compared to higher class children.
Thus, a study that shows correlation between spanking and IQ is perfectly fine. A study that purports to find causality and spanking, however, would be far-fetched.
However, hbarcat is correct. Science, particularly social science, is conducted at the micro-level, since behavior is such a complex concept. Most published studies seem to fall around the four or five variables mark with perhaps three levels per variable. Modern studies seem to be more complex with more variables than studies from 20 years ago. I'd venture to say that the advent of SPSS has something to do with that. I'd hate to sit and calculate an ANOVA by hand for a 2 x 2 x 3 x 4 study.
P.S. Damn, Talkbass has me talking about research a lot these past two weeks.
