I assume he means an R or an R^2 of 0.6-0.8. Both are measures of correlation. R^2 would be the percent in the variation of one twins intelligence predicted by the intelligence of the other twin.
I assume he means an R or an R^2 of 0.6-0.8. Both are measures of correlation. R^2 would be the percent in the variation of one twins intelligence predicted by the intelligence of the other twin.