A colleague sent me this note.
>A statistics question.
>
>Temperatures taken from different portions of a stream:
>
>Portion 1
>16.9
>17
>15.8
>17.1
>18.7
>18
>
>mean = 17.25
>variance = 0.995
>
>Portion 2
>18.3
>18.5
>
>mean = 18.4
>variance = 0.02
>
>Do these portions have different temperatures?
>
>Obviously the variances are unequal and a 2-sample [unequal variance]
t = 2.74 w/ 5 df p = 0.037.
>No problem.
>But (and this is where I am perplexed), a pooled [equal variance]
t = 1.54 w/ 6 df p = 0.17.
>Why is the less conservative pooled t giving a lower t-value? Are the
>variances so uequal (and the one so close to zero) that the formula is
>messed up?
I have a hunch that his hunch is probably correct, if inexactly formulated.
Any insights you can offer? Thanks.
--------------------------------------------------------------------------
Richard S. Lehman [EMAIL PROTECTED]
Professor of Psychology (That's R-underscore-Lehman)
Department of Psychology
Franklin & Marshall College Voice (717)291-4202
PO Box 3003 FAX (717)291-4387
Lancaster, PA 17604-3003
"I'd rather be blowing glass."
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