[Air-L] A question for researchers interested in the basics of statistical inference

[Monica Barratt]

continued from previous message...

In response to Fred Stutzman:
I won't re-quote half of your response although it was all very useful to
me. I would be most grateful for any text/reference you can provide that
discusses the use of inferential statistics on a purposive sample - "to draw
inference about relations in data".

Again, maybe I am missing a piece of the puzzle, but why use inferential
statistics to draw inferences about the relations between variables when we
can just measure them - if we are assuming the sample is the population. Eg.
I ask of my data, are monthly+ ecstasy users younger than occasional ecstasy
users? and I find regular users are, for example, mean age 20 compared to
mean age 25 for occasional users. Because I don't know the bias in my
sample, I don't know if this will be wildly different with another sample of
this population, so I could just report the two means and note the
difference. Although it makes my research look more sophisticated with the p
value (and even confidence intervals around those means), I'm not convinced
that it makes sense to include them!

In response to Peter Timusk:

Sorry if that came across as absolute in my original post - of course there
are examples of probability samples of drug users. These are generally the
exception rather than the norm, though. And I would not seek to generalise
to a wider population of drug users from my sample - I'm really just
interested in understanding them as a population, knowing they would differ
in substantive ways from more general populations of people who use drugs.

As for the size of the sample, again, I'm concerned that the size of the
sample is less of an issue than the way it is sampled. Having a larger
sample with unknown bias is still a sample with unknown bias!

Thanks again (and sorry for the rather long post)

Monica