Psychology 206 – Class Notes – 11/7/08
Went from Zscores to correlation
…going back to Z scores to hypothesis testing
Standard Normal Curve
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Mean is 0
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Std. dev. Is 1
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Area under the curve – proportion of scores
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Area under the curve (100) = percent of scores
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Area under the curve = probability of a single score
A puzzle
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IQ is normally distributed with µ=100 and (pop. Std. dev. = 16)
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A class of N=28 children take an IQ test and obtain a M=106.3
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Evidence of “foul play”?
(Is this sample beyond the acceptable range?)
Did the
sample come from the general population?
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In other words, how likely is it that a sample of N=28 scores would have a mean
of 106.3 when the µ=100 and (pop. Std. dev = 16)?
Is this sample Likely to be part of the general population?
Or,
Is it unlikely to be part of the general population?
Is there evidence of foul play?
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WE HAVE A FORMAL WAY TO DECIDE!
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This formal method is a
Ztest
o
We use the Z test when we have:
1 sample and therefore 1 sample mean
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 Fall '07
 KenneyBenson
 Psychology, Normal Distribution, general population, Std. Dev

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