person identifier
1980 to 1987
=1 if black
=1 if married
years of schooling
=1 if in union
=1 if year == 1981
=1 if year == 1982
=1 if year == 1983
=1 if year == 1984
=1 if year == 1985
=1 if year == 1986
=1 if year == 1987
union in 1980?
union[_n-1]
time avg. of married
educ*union80
married in 1981?
married in 1982?
married in 1983?
married in 1984?
married in 1985?
married in 1986?
married in 1987?