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Unformatted text preview: sing sA or sB, but we get a better estimate by using all of the data. The formula for sample variance from a single sample is the average of (X – M)2, and when we have two samples we do essentially the same thing. 2 MS = # A ( X " M A ) + #B ( X " M B )
df 2 (3) In this formula, the ∑A symbol means sum over all of Sample A, and ∑B means sum over all of Sample B. Notice that (X – MA)2 or (X – MB)2 for each individual score is an estimate of !
the population variance, σ2, and all Equation 3 does is average these estimates to get one single best estimate for σ2. The degrees of fre...
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This document was uploaded on 02/25/2014 for the course PSYC 3101 at Colorado.
 Spring '08
 MARTICHUSKI
 Psychology

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