Extreme nonresponse and response bias

The article analyzes response bias in the Norwegian Monitor, a series of surveys carried out every second year since 1985, with a response rate of only 4 % in the last wave. One third of the respondents in a telephone interview completed the follow-up mail questionnaire. Their answers in the telephone interview are compared with those of the total telephone sample. Furthermore, results from the mail questionnaire are compared with population statistics and high-response surveys. Finally, the plausibility of nonresponse bias as an explanation regarding trends and correlations in the data is discussed. The conclusion is that even in this extreme case of nonresponse most results are not biased, suggesting that also survey data with very low response rates may have scientific value.