- #1

RichS

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I've been given a set of samples, each has different sample size and mean (but not individual observations). I'm trying to figure out the population standard deviation so that I can estimate required sample size for certain confidence intervals.

My question is how do I do this? The standard textbook formula is:

StDev of population = StDev of means (standard error) * sqrt(sample size)

The problem is that this formula applies to equal sample size. In my case each sample size is different. How do I do this?

Someone suggested me to look into pooled variance and intuitively I'd think it should be a form of weighted average. So would the Satterthwaite Approximation give me the standard error that I'm looking for? Even if it does, what "sample size" should I put in the above formula [StDev of population = StDev of means (standard error) * sqrt(sample size)]Many thanks,

Rich