9 Appendix B

9.1  Representativeness at baseline and sample attrition

A primary goal for the sample selection process of any national study is to ensure that the final sample accurately represents the national population which it is intended to reflect. Table 1 illustrates the degree to which the HWR Māori and non-Māori sub-samples from the baseline survey in 2006 reflect the demographic characteristics of the New Zealand 55 to 70 year old Māori and non-Māori populations, as per demographic data from the 2006 New Zealand National Census (Statistics New Zealand, 2011).[13]

Table 12 shows that both the HWR baseline sub-samples (Māori and non-Māori ) align closely with their respective New Zealand populations, as evident in the proportions of (1) participants across age groups, (2) men and women, (3) those in full time work, and (4) those with no secondary-school qualifications. However, in comparison to their respective populations, the HWR baseline sub-samples both have perceptibly higher proportions than expected of people who are (1) currently in relationships (partnered), (2) in part-time work versus retired/other, (3) tertiary educated, and (4) earning above $20,000. In this regard, as opposed to the New Zealand population aged 55-70, the HWR sample in general reflects a disproportionately greater number of New Zealanders who are still working.

Source: HWR wave 1 and 2006 Census.

Notes:

1. Sub-sample given in parentheses. These may vary from sample total due to missing data.
2. For the purposes of comparing with the Census, approximately 375 participants are excluded from the age-group analysis as they were 54 years old at the time of the wave 1 survey. This reflects the imprecision of the Electoral Roll's age-indicator which is based on participants' “birth year” rather than their specific birth-date. Four further participants were excluded from the age-group analysis, as they reported ages beyond the 70-year upper limit.
3. Secondary = high school; post secondary = trade or polytechnic; tertiary = university

The demographic characteristics of the cross-sectional baseline sample were compared with the HWR longitudinal sample characteristics at wave 2 and wave 3 (see Table 13).

These results suggest that the wave 2 sample is comprised of baseline participants who are more likely to be working, in better health, better educated and less likely to smoke, but more likely to consume alcohol. The transition from wave 2 to wave 3 highlighted an ethnicity-specific divergence in demographic hallmarks. Whereas Māori in wave 3 were more likely than attritors to be partnered, in better health, and non-smoking, the non-Māori in wave 3 were more likely than attritors to be female, educated, non-smokers and more frequent drinkers. These differences should be borne in mind when considering the results and conclusions of the analysis.