st: what does -egen std- do?

[Caleb Southworth <caleb@uoregon.edu>]

How is the variable generated by -egen std- standardized?

Here I take a variable, subtract the mean and divided by sd

gen std_man=(P_math-45.20336)/13.3137

Here's the egen version

egen std_egn=std(P_math)

. sum std*

    Variable |       Obs        Mean    Std. Dev.       Min        Max
-------------+--------------------------------------------------------
     std_man |       775    2.58e-07    .9999999  -3.019699    3.06426
     std_egn |       775   -1.24e-09           1  -3.019699    3.06426

What explains the difference in means?

Caleb Southworth
Associate Professor
Univ. of Oregon Sociology
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