Aim: To understand declining response rates in New Zealand sleep health surveys by examining contextual changes and specific aspects of the questionnaires and research design that may have contributed.
Method: From 1999-2008, four population surveys were undertaken, seeking to recruit equal numbers of Māori and non-Māori, consistent with the Kaupapa Māori principle of equal explanatory power; using the electoral roll as a sampling frame and including extensive follow-up.
Results: In successive surveys, there were fewer respondents in all age groups. Response rates from Māori were lower in all surveys and the percentage decline was greater than for non-Māori. Between 1999 and 2008, the response rates from the initial mail-out decreased by 50% and the proportion of the sample that were uncontactable increased by 50%. Identified societal trends included decreased currency of electoral roll address information, declining use of listed landline telephone numbers, and possibly declining willingness to participate from increasing respondent burden. Contributing study design features may have included changes in Māori leadership, increasing complexity of questions and saliency of the research topic to potential participants.
Conclusions: The declining response rate in sleep population surveys is likely to be due to a number of factors. The pros and cons of using the electoral roll as a sampling frame in mail surveys should be carefully considered.