Burt data frame has 27 rows and 4 columns.
The “data” were simply (and notoriously) manufactured. The
same data are in the dataset “twins" in the
package, but with different labels.
This data frame contains the following columns:
IQ of twin raised by biological parents
IQ of twin raised by foster parents
A factor with levels (note: out of order):
Burt, C. (1966) The genetic determination of differences in intelligence: A study of monozygotic twins reared together and apart. British Journal of Psychology 57, 137–153.