Case 1: Use college as an instrument for education. We have one endogenous regressor and one instrument. The reduced form equations for log(wage) and education are reported in the first and second columns of Table 12.2. Case 2: Card (1995) also points out that if education is endogenous then so is our measure of experience since it is calculated by subtracting education from age. He suggests that we can use the variables age and age 2 as instruments for experience and experience 2 . The age variables are exogenous (not choice variables) yet highly correlated with experience and experience 2 . Following this recommendation we now have three endogenous regressors and three instruments. The reduced form equations are reported in the third to fifth columns of