Unit and item nonresponse

Item nonresponse leaves a particular measurement unobserved while retaining other measurements on that individual. Unit nonresponse leaves all survey measurements unavailable. Adjusting for an observed auxiliary variable can address item nonresponse under missing at random, but does not identify the auxiliary-variable distribution among unit nonresponders. Extrapolation to them needs further assumptions or external information.

Table of contents
- Sensitivity analysis for unit and item nonresponse Unit and item nonresponse

Sensitivity analysis for unit and item nonresponse ( $θ = [n_{R} p_{R} + n_{I} p_{I} + n_{U} p_{U}] / n$ )

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Vary the unobserved outcome probabilities for item and unit nonresponders, and any unknown auxiliary-variable mixture, over scientifically plausible ranges. Recompute the population estimate and identify values at which substantive conclusions change. This probes untestable transport or missing at random assumptions; it is distinct from sampling uncertainty represented by a confidence interval. Letting each missing-outcome probability vary from zero to one gives worst-case identification bounds.