When you can't ask their names: linking anonymous respondents with the Hogben number.

This article describes a method of linking anonymous subjects with a respondent-generated code using an algorithm based on personal details to produce unique identifiers. It was used to increase confidentiality and statistical power in a year-long work-place health promotion evaluation. Subjects were employees of a large retail chain; 80 per cent were female, and the majority educated to high school level. Of the 385 possible, 81 per cent matched; 67 per cent of the codes were matched on all elements and another 14 per cent were accepted as 'fuzzy' matches. Linking respondents increased the statistical power of the study from an unacceptable 0.4 to an acceptable 0.8. Other research on linking records is briefly discussed, including sample bias and probabilistic matching. This technique is useful when anonymity is likely to raise response rates, but the ideal code could be further sought.