In medical trials subjects are very often paid. I would guess that the
response rate for a Wikipedia survey would increase if the researcher
mentioned that the subjects/survey taker would be paid.
In a survey for our "Lyngby" programming toolbox we made a lottery among
the respondents and gave away a gift card for the Amazon online bookstore
to the winner. Among the 270 registered users we got 28 responses and one
regarding our survey as spam.
Finn Aarup Nielsen, DTU Informatics, Denmark
Lundbeck Foundation Center for Integrated Molecular Brain Imaging