I am currently reading Dr. Richard Haier's book The Neuroscience of Intelligence. I have a base knowledge of statistics, but I am confused about the following extract from page 80 (chapter 2.4):
When correlations are computed in identical twins reared apart, the correlation is also one way to estimate heritability, so a correlation of .70 indicates that 70% of the variance in intelligence is due to genetic factors and 30% is not.
Is using correlation a valid way to estimate the heritability of a specific trait? I was under the impression that for a comparison of shared variance r² would have to be used, which would mean IQ is not 70% inherited, but only 49% (a huge difference!).