Various robust procedures have been developed for situations where sampling deviate from probability selection, or, when we face non-coverage and non-response problems.
This requirement lessens agency expense, practically eliminates non-response bias (a perennial headache for most private market researchers), and improves accuracy.
This would be the case, for example, if the criticism itself consisted of being there (intruding, trespassing, causing property damage), or not being there (non-response).
