Does Personality Matter? Compared to What?
According to [the meta-analysis in "The Power of Personality: The Comparative Validity of Personality Traits, Socioeconomic Status, and Cognitive Ability for Predicting Important Life Outcomes"], you can measure personality with a simple survey, then use it years or decades later to make good predictions about mortality, divorce, and occupational status.
The paper ends with three key graphs. The first shows correlations between mortality and (a) socioeconomic status, (b) IQ, and (c) four of the Big 5 personality traits:
As Caplan points out, The Bell Curve demonstrates that IQ out-predicts socioeconomic status, but apparently conscientiousness alone out-predicts IQ — at least with respect to mortality.
Are theses small correlation coefficients meaningful though? Compared to what?
Walter Mischel (1968) argued that personality traits had limited utility in predicting behavior because their correlational upper limit appeared to be about .30. Subsequently, this .30 value became derided as the ”personality coefficient.” …
Should personality psychologists be apologetic for their modest validity coefficients? Apparently not, according to Meyer and his colleagues (Meyer et al., 2001), who did psychological science a service by tabling the effect sizes for a wide variety of psychological investigations and placing them side-by-side with comparable effect sizes from medicine and everyday life. These investigators made several important points. First, the modal effect size on a correlational scale for psychology as a whole is between .10 and .40, including that seen in experimental investigations… Second, the very largest effects for any variables in psychology are in the .50 to .60 range, and these are quite rare (e.g., the effect of increasing age on declining speed of information processing in adults). Third, effect sizes for assessment measures and therapeutic interventions in psychology are similar to those found in medicine. It is sobering to see that the effect sizes for many medical interventions — like consuming aspirin to treat heart disease or using chemotherapy to treat breast cancer — translate into correlations of .02 or .03.