----- Original Message -----
From: Robert J. MacG. Dawson <[EMAIL PROTECTED]>
To: Richard Lehman <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Sent: Friday, November 03, 2000 1:16 PM
Subject: Re: Two t tests
>
>
> Richard Lehman wrote:
> >
> > 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]
................................
>From knowing the characteristics of flowing streams, one should expect
considerable variance. The concept of experimental design would enable one
to plan where to measure to obtain a reasonable mean value. The bottom, if
after a pool, will be colder, and a cross section of the stream will have
high variance. Side stream entries will result in one side being a different
temperature then the other side. A turbulent area will have less variance.
You have to determine where the measurements were made in terms of the flow
characteristics of the locality. Therefore from a practical standpoint, you
can't conclude that the two groups have different means.
DAHeiser.
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