topic calculate pooled sigma in SAS Procedures

calculate pooled sigma

chrisgo — Fri, 22 May 2015 01:42:50 GMT

given dataset below, i want to compute the pooled sigma by Group. Already tried Ttest but it is limited to two class variables

Reeza — Fri, 22 May 2015 02:26:55 GMT

Assuming sigma is standard deviation and therefore variance I would look into PROC GLM.

PS. Stats questions are best posted under Statistical Procedure forum.

stat_sas — Fri, 22 May 2015 02:30:00 GMT

data have;

input Group $ COUNT MEAN SIGMA MEAS_DATE :anydtdte.;

format meas_date ddmmyy8.;

datalines;

a 501 101.1664 12.62792 14-Apr-15

a 123 103.33 10.545 8-Apr-15

b 164 99.21071 16.14705 8-Apr-15

b 697 86.24266 9.794989 9-Apr-15

c 223 82.22 7.422 7-Apr-15

c 780 84.10039 8.913545 8-Apr-15

;

proc sql;

select *,sqrt(sum((count-1)*sigma**2)/sum(count)-count(*)) as pool_sigma from have

group by group;

quit;

Rick_SAS — Fri, 22 May 2015 17:43:37 GMT

Are you missing a set of parentheses? Seem like it should be

sqrt(sum((count-1)*sigma**2) / (sum(count)-count(*)))

stat_sas — Fri, 22 May 2015 20:15:56 GMT

Thanks Dr. Rick - Yes, we need one extra set of parentheses to formulate this correctly.

proc sql;

select *,sqrt(sum((count-1)*sigma**2) / (sum(count)-count(*))) as pool_sigma from have

group by group;

quit;