This investigation sought to determine the reasons underlying the declining response rates in New Zealand sleep health surveys, using data from four population surveys undertaken from 1999–2008. The surveys used the electoral roll as a sampling frame and sought to recruit equal numbers of Māori and non-Māori, consistent with the Kaupapa Māori principle of equal explanatory power. The survey method also included extensive follow-up. Successive surveys revealed 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. By 2008, the response rates from the initial mail-out in 1999 had decreased by 50% and the proportion of the sample classified as uncontactable had increased by 50%. Explanatory factors 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. Contributory study design features included a possible impact from a shift in leadership by a Māori health research centre to Māori researchers in a non-Māori research centre, increasing complexity of questions and saliency of the research topic to potential participants.
