This meta-analysis of adolescents and young adults given IQ tests multiple times, the risk of schizophrenia increases about 55% for each standard deviation in IQ lost. This finding should be framed appropriately, however. The risk of schizophrenia is low and remains low, even when IQ drops. Most people in whom IQ drops do not go on to develop schizophrenia. However, the risk of developing schizophrenia is higher among people whose IQ drops significantly.
This experiment assigned participants to one of three treatment conditions: 1) Heading training 2)Soccer training without heading 3) No treatment control. Neuropsychological tests of attention and working memory failed to show any short-term negative effects of heading training (other than more headaches in female participants). Interpretation of this study should be interpreted cautiously: There may be long-term effects of heading that the study was not designed to measure.
This meta-analysis found that simple memory span measures (e.g., Digits Forward) and complex span measures correlate more strongly in adolescents than in children. Eyeballing Figure 1 in the paper, it appears that the correlation increases from about 0.35 at age 5 to about 0.45 at age 20. It does not appear that the finding is an artifact of reliability. The interpretation of the finding is that both types of tests require storage ability and executive ability but in differing proportions. The author of the paper proposes that the executive control of attention in children develops considerably throughout childhood and adolescence whereas the storage capacity of primary memory stays comparatively more stable over time. Thus, performance on simple memory span increases over time mostly as a function of the maturation of executive ability. Thus, simple span measures correlate more strongly with complex span measures (which measure executive control of attention more directly) in older samples than in younger samples.
This longitudinal study of older adults suggests that cognitive declines in late adulthood were steeper for earlier-born cohorts (born 1886-1913) than for later-born cohorts (born 1914-1946).
I read a 2005 chapter by Scarborough today. It was a good quick read about how the relationship between phonological processing deficits and reading problems is more complicated than we might wish it to be.
Kevin McGrew posted a link to a recent paper by Byington and Felps (2010) proposing an alternative explanation for the relationship between IQ and job performance. Actually it is a supplementary explanation. The authors grant that there is some link between IQ and job performance that is likely to be there whether institutions select on it or not. However, this relationship is intensified by institutional practices that allocate educational and other resources by IQ and IQ-like tests. That is, if you give job skill-enhancing experiences to people who score high on tests, the correlation between job performance and IQ will increase.
I cannot imagine that this self-fulfilling correlation effect is not present. In fact, I can imagine members of committees that hand out merit scholarships thinking, “Of course, this is exactly what we are trying to promote! We have been doing this explicitly for a long time. Did we really need a new paper to ‘reveal’ this to us?”