Too good to be true? The late English psychologist Cyril Burt was known for his studies of the IQ scores of identical twins who were raised apart.

The high correlation between the IQs of separated twins in Burt’s studies pointed to heredity as a major factor in IQ. (“Correlation” measures how closely two variables are connected. We will meet correlation in Chapter 14.) Burt wrote several accounts of his work, adding more pairs of twins over time. Here are his reported correlations as he published them:

Publication date Twins reared apart Twins reared together 1955 0.771 (21 pairs) 0.944 (83 pairs)

1966 0.771 (53 pairs) 0.944 (95 pairs)

What is suspicious here?