Type A personality in Australian twins.

We examined the genetic and environmental determinants of Type A behavior in 200 pairs of same-sex twins as measured by the structured interview (SI) of Rosenman and Friedman and by the Bortner questionnaire (BARS). As noted previously, these measures are poorly correlated (r = .30). Quite different heritabilities were found for the two measures (63% for SI, 23% for BARS), and the correlation between the two was found to be largely genetic. Although the sample size meant that differences in correlation between MZ and DZ twins on the BARS were not significant in univariate analyses, they were suggestive of twin competition effects, as other twin studies have found. We conclude that further genetic analyses should concentrate on component behaviors rather than the overall Type A construct.