Speculatively, temperature could confound or be a rival hypothesis in a few ways.
It would influence what could be in solution, pollutants as well as things that
offset them. It could be what varies across the parts of rivers or between rivers.
It might differentially influence survival or breeding of different species. etc.
Jay Tanzman wrote:
> Art Kendall wrote:
>
> [snip good points]
>
> > in your quasi-experiment you can possibly contrast different levels of specific
> > pollutants, as well as kinds of pollutants, in different rivers at different
> > times.
> > I'm not a biologist, but I would be amazed if temperature did not affect
> > population sizes.
>
> Yeah, but would temperature also be related to pollultion levels, and if not, so
> what if it is related to the outcome under study.
>
> -Jay
=================================================================
Instructions for joining and leaving this list, remarks about the
problem of INAPPROPRIATE MESSAGES, and archives are available at
http://jse.stat.ncsu.edu/
=================================================================
