SSCHEINE wrote:
>
> Let me take a (somewhat) contrarian position to those previously
> expressed. An experiment is any test of a hypothesis. An experiment can
> involve the use of observational (unmanipulated) data, as long as the
> hypothesis is clearly stated prior to the collection of the data. While
> it is true that an experiment involving manipulation can provide some of
> the best evidence for causal relationships, causal relationships can be
> deduced from observation data combined with other information about how
> the world works.
I agree that you can test a hypothesis by using an observational study, but that
does not make it an experiment. The original poster was looking for a
definition to use in a lecture, and an experiment, by definition, involes
assignment of treatments to experimental units.
> All of that said, the situation described below is what I would call a
> hypothesis-generating activity. That is, you want to look for a
> potential correlation that you will use to then test specific mechanisms
> (i.e., doex chemical X kill fish?). It would be a hypothesis-testing
> activity, if you had a prespecified hypothesis concerning a particular
> pollutant that previous experiments have shown to kill or otherwise harm
> fish.
A study is hypothesis testing if the investigator is using it as such. Whether
the particular study design would be expected to yield a valid answer is another
matter.
-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/
=================================================================
