The problem with people who don't fill in surveys

Someone must have written a paper on this. Can't be arsed to look for
it. It'd probably make my point more authoritative.

Surveys in academia can get very high response rates compared to
commerical surveys. 60% and even 70% responses rates are expected for
high quality studies.

The results from a survey of 70% of the population can't be assumed to
represent the result for the whole population. What I'm guessing and
what has been guessed before in papers I've read is that there will be a
higher degree of negative results within the non-responders.

For qualitative and quantitative researchers who want high quality
results this is a serious problem.