nonrespondents

Nonrespondents are individuals or units selected for a study who do not participate in data collection efforts. In survey research, they may be unreachable, refuse to participate, or be ineligible, and their absence can affect the completeness and representativeness of the data.

Two related concepts are unit nonresponse and item nonresponse. Unit nonresponse occurs when a sampled unit provides no data at all, while item nonresponse occurs when respondents skip or refuse to answer specific questions. Both forms can reduce the effective sample size and introduce bias if nonrespondents differ systematically from respondents on key variables.

Causes of nonresponse include coverage gaps in the sampling frame, contact difficulties, language barriers, time constraints, privacy concerns, and reluctance to disclose information. Nonresponse tends to be higher among certain groups, such as busy individuals, younger or lower-income respondents, or those with particular attitudes toward the survey topic.

Impact depends on whether nonrespondents differ from respondents in meaningful ways. When differences exist, nonresponse can bias estimates, particularly for statistics related to the variables used to model response and for subgroups with higher nonresponse.

Measurement and mitigation involve tracking response and cooperation rates, documenting methods, and applying adjustments. Practices include follow-up contacts, mixed-mode data collection, incentives, and tracking efforts. Statistical remedies include weighting adjustments, response propensity modeling, and imputation for item nonresponse. Researchers may also conduct nonresponse bias analyses by comparing early versus late respondents or using external benchmarks, and they often report transparency about limitations due to nonresponse.