Nonresponse bias

Nonresponse bias occurs when people who do not participate in a survey or study differ systematically from those who do, skewing estimates.

Survey nonresponse: Survey nonresponse occurs when selected participants do not provide the requested information. It is the participation failure that can produce nonresponse bias.
Survey sampling: Survey sampling selects a subset of a population to estimate characteristics of the whole. Nonresponse bias alters the intended inference from a sample to its population.
Nonresponse follow-up: Nonresponse follow-up is additional contact with sampled units that have not yet participated. Follow-up can recover responses and reveal how initial nonrespondents differ.
Nonresponse error: Nonresponse error is the total error associated with missing survey responses, including bias and increased variance. It is broader than nonresponse bias and includes uncertainty from fewer completed cases.
Unit nonresponse: Unit nonresponse occurs when a sampled person or organization provides no usable data. Entire missing cases create the bias considered here.
Selection bias: Selection bias arises when inclusion in an analysis is related to characteristics affecting its results. Nonresponse bias is a specific form of bias caused by selective participation.
Response rate: A response rate is the proportion of eligible sampled units that provide survey data. It measures participation, but a low rate alone does not establish bias.
Coverage error: Coverage error occurs when a sampling frame omits, duplicates, or incorrectly includes members of the target population. It concerns who could be selected, while nonresponse bias concerns who participates after selection.
Item nonresponse: Item nonresponse occurs when a participant leaves one or more questions unanswered. Missing answers can bias particular estimates even when participants otherwise respond.
Sampling bias: Sampling bias occurs when a sample systematically differs from its target population because of selection procedures. It can precede nonresponse, and the two distortions require different remedies.

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