1 = 1st born (includes only children)
2 = middle child
3 = last born (includes 2nd of 2)

Social Class Background (as measured by parents' average years of schooling)
1 = lower class (less than 10.5 years)
2 = middle class (10.5 to 12 years)
3 = upper class (more than 12 years)

0 = male
1 = female