Fig. 1.

Regression coefficient and 95% CIs using a random-effects model with height as the dependent variable and twin type as the independent variable for females. The effect size shows the increase in height of OS females as compared to dizygotic SS females. If the twin testosterone hypothesis were supported, the effect would be in the positive direction, and the effect size would be significant. The results are adjusted for age and birth year and the non-independence (clustering) of observations within twin pairs. Squares indicate study-specific regression coefficients, and the size of the squares is proportional to the weight of each study, i.e., the inverse of the variance. The horizontal lines represent 95% CIs