Posted by Katty on Monday, October 3, 2011 at 1:50am.
What do you mean by unusual? P < .10? P < .05? P < .01?
Z = (mean1 - mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√(n-1)
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion for that Z score.
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