Term	Imputation
Synonym
Related Term
Source of Definition
Short Definition
Statistical Activity	Survey design

Definition
If there is any non-response in a survey we must impute, whether implicitly (by rating up) or explicitly (by unit record imputation). Rating up is when the estimate is derived from the achieved sample with the weights adjusted accordingly.
The most common kinds of unit-record imputation are cell-average imputation and historical imputation. Both of these methods incorporate auxiliary information about the non-respondent.

Example
A unit does not respond to the survey. Their previous value was 20 and similar units have doubled their values since the previous period, so we impute a value of 20 x 2 = 40 for the non-respondent. (This is called weighted historical imputation).