* Nonexperimental Regression;

data nonexp;

 label ach6='reading achievement(6th grade)'

       apt='a measure of verbal aptitude(5th grade)'

       att='a measure of attitude toward school(5th grade)'

       income='a measure of parental income($1000);



id     ach6     ach5      apt     att  income

---------------------------------------------

 1      7.5      6.6      104      60      67

 2      6.9      6.0      116      58      29

 3      7.2      6.0      130      63      36

 4      6.8      5.9      110      74      84

 5      6.7      6.1      114      55      33

 6      6.6      6.3      108      52      21

 7      7.1      5.2      103      48      19

 8      6.5      4.4       92      42      30

 9      7.2      4.9      136      57      32

10      6.2      5.1      105      49      23

11      6.5      4.6       98      54      57

12      5.8      4.3       91      56      29

13      6.7      4.8      100      49      30

14      5.5      4.2       98      43      36

15      5.3      4.3      101      52      31

16      4.7      4.4       84      41      33

17      4.9      3.9       96      50      20

18      4.8      4.1       99      52      34

19      4.7      3.8      106      47      30

20      4.6      3.6       89      58      27