Dale Berger wrote:
>
> Adding to Art's list:
> If one has email addresses for a population of interest and
> wishes to collect information that is not particularly
> sensitive, an internet format might work as well or better
> than a mail survey.
Yes. However, those called "internet" rather than "email" surveys are
usually those that involve putting up a form on a web page and waiting
for a Heffalump to fall into it. IIRC, the original question dealt with
concerns such as whether other users could access the responses that
only make sense in such a context. The best that can be said for _these_
is that they might work as well or better than the Shere Hite style
questionnaire- in- a- magazine survey.
> There would still be
> problems of inference if the response rate was low
Indeed. And "low" does not mean less than 10% of the sample, it means
less than (say) 90% of the _population_. The nonrespondents must be too
few to matter. This is a nonrandom sample, and the beginner's intuition
that a small sample cannot represent the whole is _correct_ for such.
If the starting address list is truly randomized within the population,
things are a little better; in such a case, 90% or so of the address
list may be enough. It would also be enough if the address list were
chosen in a way that had no plausible connection to the question at
hand.
Now, all this is verifiable. If the researcher using email (or snail
mail, or telephone interviews - pick your technology level) for a survey
can verify that the address list is randomly chosen from a well-defined
sampling frame, and that the nonresponse rate is low enough not to
affect the inference, the results may be usable.
However, is this going to be the case? If in fact the address list is
chosen for convenience and may be significantly nonrandom, will the
study go ahead anyway? If the nonresponse rate is 75% - or even 50% or
25% - will the study be dropped? If results are published, will they be
titled "Perceptions of Innumeracy Among American College Graduates" or
"Perceptions of Innumeracy Among Euphoric State University Alumni Who
Gave Their Email Addresses To The Alumni Office And Choose To Answer A
Certain Survey?" Only the latter would be accurate.
The problem is very simple. Random sampling is a powerful technique
that allows us - despite the intuition of many intelligent people
without a statistical background - to make valid inferences from a small
sample to a larger population.
Nonrandom sampling is not; to do it, and to expect it to have the same
results as random sampling, is like building an airplane out of straw
and expecting it to fly.
-Robert Dawson
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