Pooled Standard Deviation

A weighted average of standard deviations for two or more groups.

\( SD_{pooled} = \sqrt { \frac { (n_{1}-1)SD_{1}^2+(n_{2}-1)SD_{2}^2 } { n_{1} + n_{2}-2 } } \)

Variable	Description
n₁	Number of Data points in group 1
n₂	Number of Data points in group 2
SD₁	Standard deviation of group 1
SD₂	Standard deviation of group 2

\( SD_{pooled} = \sqrt { \frac { (n_{1}-1)SD_{1}^2+(n_{2}-1)SD_{2}^2 } { n_{1} + n_{2}-2 } } \)

SDPooled

= √

(

n1a

- 1) *

SD1

+ (

n2a

- 1) *

SD2

n1b

n2b

-2