To assess nonresponse bias in a mixed‐mode general population health survey.
Secondary analysis of linked survey sample frame and administrative data, including demographic and health‐related information.
The survey was administered by mail with telephone follow‐up to nonrespondents after two mailings. To determine whether an additional mail contact or mode switch reduced nonresponse bias, we compared all respondents ( = 3,437) to respondents from each mailing and telephone respondents to the sample frame ( = 6,716).
Switching modes did not minimize the under‐representation of younger people, nonwhites, those with congestive heart failure, high users of office‐based services, and low‐utilizers of the emergency room but did reduce the over‐representation of older adults.
Multiple contact and mixed‐mode surveys may increase response rates, but they do not necessarily reduce nonresponse bias.