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Pooled standard deviation is a way of calculating the variance of multiple populations with different means but same variance. Formula for measuring pooled SD is given below: 1. Normal 2. Cohen's formula 3. For three or more groups 4. For equal sample size

Pooled standard deviation is the weighted average standard deviation for two or more independent groups. Larger samples are given more weight in decision. There are two method of calculating pooled-standard deviation: 1. 2. 2nd method is supportive only when sample size is same for individual groups. lets us understand impact of both methods with the help of examples: Suppose we have four individual groups of solar cell efficiency with same sample sizes ( shown in below table). Pooled standard deviation value will be “ 0.061826” by using first method . If we use second method then pooled standard deviation value will also be “0.061826” . Both methods are showing same pooled standard deviation value because 1st and 2nd methods will perform same in case of same sample sizes. To discern between both methods, let's change sample size of Group-1 from value "6" to "5" and let's check pooled standard deviation for both methods. Now it shows different pooled standard deviation due to sample size non-equal for individual groups. In this case pooled-std deviation value " 0.0634" is acceptable. it indicates that "more weight given to larger samples".