e is a term used in the calculation of survey response rates; it represents the proportion of sampled cases with unknown eligibility that are estimated to be eligible cases.

To determine response and other outcome rates for surveys, all cases in the sample first need to be classified into one of four categories: (1) completed cases; (2) eligible cases, no interview (nonrespondents); (3) cases of unknown eligibility, no interview; and (4) not eligible cases (out of sample). Then the eligibility status of the unknown cases needs to be estimated. The proportion of unknown cases that is estimated to be nonrespondents (i.e. eligible cases with no interviews) is known as the e-rate and is represented as e in equations. For example, in the formula for Response Rate ...