Nonresponse

Nonresponse is the failure to obtain usable information from a selected unit in a survey or study. It can occur at the level of the entire unit, known as unit nonresponse, when a sampled individual or organization does not participate at all, or at the item level, known as item nonresponse, when a participant answers some questions but declines or omits others. Nonresponse is a major source of missing data and can contribute to nonresponse bias if respondents differ systematically from nonrespondents regarding the variables of interest. The response rate, defined as the proportion of sampled units that provide usable data, is a common summary measure, but it does not by itself determine the presence or magnitude of bias.

Causes of nonresponse include contact difficulties, refusals, ineligibility, and attrition in longitudinal studies. External factors such as survey mode, timing, topic sensitivity, and respondent burden can increase nonresponse. The consequences include reduced statistical power and the potential for biased estimates, especially when nonresponse is not random with respect to key study variables.

Mitigation strategies combine survey design and data analysis. In design, researchers aim to maximize contact attempts, offer multiple modes of response (for example, web, telephone, or mail), ensure confidentiality, and minimize respondent burden with user-friendly questionnaires and appropriate incentives. In analysis, weighting adjustments, post-stratification or propensity score weighting, and imputation of missing item responses can help address nonresponse. Transparent reporting of response rates and the potential for nonresponse bias is recommended to inform interpretation and generalizability of results. Handling nonresponse thus involves both proactive design choices and careful analytic techniques to produce more accurate and generalizable conclusions while acknowledging limitations from missing data.