The Australian twins study didn't look at income. They looked "two-digit occupation" codes. Also whether you use monozygotic or dizygotic twins matters. See

The Australian twins study didn't look at income. They looked "two-digit occupation" codes. Also whether you use monozygotic or dizygotic twins matters. See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3359051/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3359051/ When just looking at monozygotic twins, ones that don't attend university actually make more money.