Thanks for your comment. The message was accidentally sent from my wife's
news account.
I didn't take the measurement simultaneously, but it is not my major
concern. My concern is: I did a regression on the mean(WT) against
mean(AT). Is this good enough? Can I get more out of data? I've been
trying to get QVF(Quasiliklihood estimation model from stat.tamu.edu) and
some multivariate delta SAS macro to work. They seems too complicated for
such a simple situation. Is there a simple way?
Thanks again for your help.
Cheers,
Wenjing Dai
([EMAIL PROTECTED])
Department of Computer Science, University of Illinois
"Donald Burrill" <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> On Fri, 9 Mar 2001, Wei Xiao wrote:
>
> > Suppose I went to 10 lakes. I want to measure the relation with water
> > temperature (WT) and air temperature (AT). So I can do a regression
> > with these 10 points like this:
> > | *
> > | * AT
> > | *
> > |__*__________________
> > WT
> >
> > However, to be sure, I took 3 AT's and 3 WT's at each lake. Now any
> > particular AT is not correlated with WT.
>
> How can that be? Did you not take each AT and WT at the same time and
> in the same place? (Not necessarily at the same time, or in the same
> place, as the other pairs of (WT,AT); in fact, preferably the
> measurements should have been made at different (time, place) if what
> you were trying to do was to get a measure of the variability in WT
> and AT at each lake.)
> If you claim they're not correlated because all six values were taken
> more or less simultaneously at the same place, and they were not taken
> in (WT,AT) pairs, then the three WT values are not independent
> observations, nor are the three AT values, but within each of THESE
> triplets the values are correlated in an unknown, and possibly
> unknowable, way. Then all you can do is take the easy way out:
> take the average of the three WT values as the WT for that lake,
> and similarly for the three AT values.
>
> > Instead, they are kind of have error in both X and Y axis.
>
> This remark is not helpful. If you only had one value of (WT,AT) at
> each lake, those values would surely have measurement error in both
> measurements.
>
> > Can somebody show me a better way to analyze this?
> > I prefer talking in SAS or SAS macro.
> Sorry, not one of my languages.
>
> > Here is hypotheticall data sheet.
> > Lake, WT, AT
> > Lake1 10 15
> > Lake1 11 14
> > Lake1 12 13
> > ...
> >
> > Notice there is no relation between WT and AT reading.
> > I can record this way too:
> > Lake, WT, AT
> > Lake1 10 13
> > Lake1 11 14
> > Lake1 12 15
> > ...
>
> It is not at all clear why you can legitimately shuffle these values
> around with respect to each other: unless either (a) all 6 values are
> recorded simultaneously in the same place; or (b) you took all 6
> values at 6 different times and places, so that there really is no
> empirical connection between any particular AT and any particular WT.
> Either case would seem to me to represent faulty experimental
> procedure... to put it politely.
> -- DFB.
> ----------------------------------------------------------------------
> Donald F. Burrill [EMAIL PROTECTED]
> 348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED]
> MSC #29, Plymouth, NH 03264 (603) 535-2597
> 184 Nashua Road, Bedford, NH 03110 (603) 471-7128
>
>
>
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