We can rewrite the formula for s so that its a sum of

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Unformatted text preview: ate, ! the MS in Equation 3, is the average of nA numbers from Sample A and nB numbers from Sample B. However, because the formula depends on MA and MB, which are both computed from the data, we “lose” two degrees of freedom. Independent ­samples t ­test: df = n A + n B " 2 (7) Degrees of freedom in general. Any Mean Square formula is an average of numbers of the 2 ˆ ˆ form X " X , where X is some statistic like M. The question is, how many numbers are ! we really averaging? The answer isn’t what it naively seems to be, and this is why we need the concept of degrees of freedom. ! Take the sample variance as an example. Sample variance is the simplest v...
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This document was uploaded on 02/25/2014 for the course PSYC 3101 at Colorado.

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