st: standardizing scores by cohort

[Paul Byatta <paulbyatta@gmail.com>]

Hi

I am trying to standardize raw
scores for several cohorts of students based on year of admission to high
school.

My data looks like this


StudentID    Year of                   math
                   Admission (yoa)

1                  2004                     78
2                  2004                     83
3                  2004                     99
4                  2005                      58
5                  2005                     68
6                  2005                     67
7                  2006                     87
8                  2006                     75
9                  2006                    56

It would have been easier to use


egen std_math =3D std(math) by yoa

But then egen doesn=92t go with =93by=94 in this case.

Anybody with a suggestion of how standardize the scores without having to
through the long process that is (below) and combining the generated
variables to get std_math?



egen std_math4 =3D std(math) if yoa=3D=3D2004
egen std_math5 =3D std(math) if yoa=3D=3D2005
egen std_math6 =3D std(math) if yoa=3D=3D2006

Thanks

Paul
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