GMACRO
NEGD1
Random 500 C1;
Normal 50 5.
Random 500 C2;
Normal 0 5.
Random 500 C3;
Normal 0 5.
Add C1 C2 C4.
Add C1 C3 C5.
Name C1 ='true' C2 ='x error' C3 ='y error' C4 ='pretest' C5 ='posttest' 
Set C6
1:500
End
Code (1:250) 0 C6 C6
Code (251:500) 1 C6 C6
Name C6 = 'Group'
Table C6 
Sign C6
Histogram 'Group'
Table C6; 
means C4 C5.
Let C4 = C4 + (5 * C6)
Let C5 = C5 + (5 * C6)
Table C6;
means C4 C5;
stdev  C4 C5.
Let C5 = C5 + (10*C6)
Table C6;
means C4 C5;
stdev  C4 C5.
Histogram C4
Histogram C5
Plot C5 * C4;
symbol.
Plot C5  * C4;
Symbol C6.
Regress C5 2 C4 C6
ENDMACRO