nonresponse
n. a participant’s failure to answer one or more survey, questionnaire, or test items or to provide a measurement on some study variable. If data values are missing completely at random, then nonresponse does not distort results. In most research situations, however, nonresponse is not a purely random phenomenon; participants who do not answer questions differ in some important, systematic way from those who do answer. The basic method for compensating for such nonresponse (or nonresponder) bias involves estimating the probability that each sample case will become a respondent.