I want to compute the pooled sigma (standard deviation) for the below-mentioned group: Group Count Mean Sigma A 2 661.7 45.3 B 2 18.06 1.64 C 2 191.4 1.41 D 2 5.51 0.352 E 2 37.265 0.898 I have calculated it using the below-mentioned program in SAS. The result I am getting for pooled sigma in SAS is 20.2864. I verified this pooled sigma value for the same dataset using Minitab and the Minitab output for pooled sigma is 20.2686 which is slightly different than the one I am getting in SAS using the below-mentioned PROC SQL program (got it from SAS help). ------------------- data Deba; input group $ Count Mean Sigma; datalines; A 2 661.7 45.3 B 2 18.06 1.64 C 2 191.4 1.41 D 2 5.51 0.352 E 2 37.265 0.898 ; proc sql; select *,sqrt(sum((count-1)*sigma**2) / (sum(count)-count(*))) as pool_sigma from Deba quit; ------------------------- I am wondering why the Minitab and SAS values are not matching? In MINITAB I am feeding the raw data which is giving me pooled sigma of 20.2686, whereas in SAS I am feeding the above-mentioned data group as I don't know the whole program in SAS to calculate the pooled sigma from my raw data. Could this be a reason for the difference in MINITAB and SAS results? OR Do I need to use a different formula for pooled sigma? My raw data is below- Groups Results A 693.70 A 629.70 B 19.22 B 16.90 C 192.40 C 190.40 D 5.76 D 5.26 E 36.63 E 37.90 Request if anyone could please help me with this.
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