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Re: st: standardizing scores by cohort


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: standardizing scores by cohort
Date   Wed, 24 Apr 2013 12:32:21 +0100

Statalist software here can't represent the equals sign = in your post
correctly. I guess that, contrary to request, you are not sending
plain text to the list.

That aside

egen mean_math = mean(math), by(yoa)
egen sd_math = sd(math), by(yoa)
gen std_math = (math - mean_math) / sd_math

should be simpler than the dreaded alternative. Note that a -by()-
option is supported, although not documented, by -egen-'s -mean()- and
-sd()- functions, but your indicated syntax

... by yoa

certainly would not work.

Nick
njcoxstata@gmail.com

On 24 April 2013 12:15, Paul Byatta <paulbyatta@gmail.com> wrote:

> 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
>
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