topic Re: Obtaining the SD per observation in SAS Programming

Obtaining the SD per observation

l_gutierrez1808 — Tue, 29 Sep 2015 02:32:31 GMT

Hi!

Given a dataset sorted by PID (ID of each participant, N=77) with several continuous variables.

I want to obtain which are the observations (PID) with values > 2 SD from the mean.

I am working with data in a temporary dataset called -- cortical_stroke_complete2

The variable of interest is : PCh_CONTRA_entorhinal_tck

This is the code that I have been trying without success, I tried different variables and always obtained the same PID.

proc sql noprint;

select mean(PCh_CONTRA_entorhinal_tck) into : mean from cortical_stroke_complete2;

select std(PCh_CONTRA_entorhinal_tck) into :std from cortical_stroke_complete2;

quit;

data cortical_stroke_complete2;

set cortical_stroke_complete2;

where PCh_CONTRA_entorhinal_tck >&mean+2*&std ;

proc print;run;

Basic SAS programmer.

Thank you so much!

Re: Obtaining the SD per observation

PGStats — Tue, 29 Sep 2015 03:03:43 GMT

No need for macros to do that. Try this

proc sql;
select *
from cortical_stroke_complete2
having PCh_CONTRA_entorhinal_tck - mean(PCh_CONTRA_entorhinal_tck) > 2*std(PCh_CONTRA_entorhinal_tck);
quit;

(untested)

Re: Obtaining the SD per observation

Astounding — Tue, 29 Sep 2015 23:50:58 GMT

Getting the same PID each time does not mean anything is wrong. It is possible that only one patient has outlier values.

When looking for values more than 2 standard deviations from the mean, you may have to consider two standard deviations in both directions.

where (PCh_Contra_entorhinal > &mean + 2*&std) or (PCh_Contra_entorhinal < &mean - 2*&std);

If you suspect this is not giving you the right result, print &mean and &std, and inspect 20 lines of data to see if you can confirm whether the result should be different.

Good luck.