- "in the relatively rare cases where parents miscategorize their twins as MZ instead of DZ (or the converse), differences in correlations of cognitive ability and personality persist"\cite{CESARINI_2010}
- (This is my personal favorite because it's the most brazen) "Perhaps the most empirically rigorous method of assessing the validity of the EEA is through the use of misclassified twin samples."\cite{BARNES_2014}
How exactly do these studies work? Fosse et al. (2015) explain: "The assumption in these studies is that if it is the parents’ treatment of the twins and not the twins’ genes that is etiologically important, then fraternal twins that are misclassified as identical should correlate higher for mental disorders than twins correctly classified as fraternal, whereas identical twins misclassified as fraternal should correlate lower than correctly classified identical twins."\cite{Fosse_2015} In other words, consider the table below, where all four letter values are correlations. If the EEA is invalid, then c should be higher than d, whereas a should similarly be higher than b.
Actually MZ | Actually DZ |
Perceived MZ | a | c |
Perceived DZ | b | d |