3 Data

The datasets used in this paper are from the Health, Work and Retirement (HWR) study and its successor, the New Zealand Longitudinal Study of Ageing (NZLSA). The HWR study was funded by the Health Research Council of New Zealand for two waves of data collection in 2006 and 2008, and was run by researchers at Massey University. The NZLSA study is funded by the Foundation for Research, Science and Technology (now the Ministry for Science and Innovation) for two waves of data collection in 2010 and 2012, and is run by the same research team at Massey University in conjunction with a research team from the Family Centre Social Policy Research Unit.

The baseline HWR survey consists of a large cross-sectional sample of New Zealanders aged over 50, who consented to participate in the 2006 postal data collection wave. A total of 5,260 adults (including Māori) were randomly selected from the New Zealand Electoral Roll to represent a general population sample. From those still remaining on the electoral roll, 7,780 Māori adults were then randomly selected (using the Māori descent indicator on the roll) specifically to increase the Māori sub-sample. Māori over-sampling was undertaken to combat the historically poor research participation rates found in older ethnic minority populations.

As a result, 13,040 New Zealanders received an HWR study questionnaire and an invitation to participate in the study. Subsequently, 551 individuals (210 from the general population sample and 341 from the Māori sub-sample) were excluded from participation due to ineligibility (eg, deceased, institutionalised, or un-contactable), thus lowering the potential participant pool to 12,489. Of this revised total, 6,657 (53%) participants returned surveys in 2006; 3,104 (61%) from the general population sample and 3,553 (48%) from the Māori population sub-sample.

The HWR 2006 (henceforth baseline) survey was considered a cross-sectional study for recruitment purposes, consent to participate in the HWR 2008 data collection wave (henceforth wave 2) was not a stipulation of baseline participation. The longitudinal sample was instead gained with a specific request at the end of the baseline questionnaire for participants to participate in the wave 2. Almost half of the 2006 HWR baseline sample (N = 3,111) subsequently consented to take part in the longitudinal section of the study, and 2,471 (79%) returned completed questionnaires in the 2008 data collection wave.

The NZLSA survey began in 2010, and subsumed the longitudinal sub-sample of the HWR project. A total pool of 4,339 older New Zealanders were provided with questionnaires and invited to complete the first NZLSA postal data collection wave in 2010 (henceforth wave3). This pool consisted of:

• the 2,471 HWR participants who participated in 2008
• 839 participants from an existing cross-sectional study of retirement planning at Massey University
• 238 from the NZLSA pilot study conducted in 2009
• 165 HWR cross-sectional participants from 2006 who consented to re-enter the study
• 683 New Zealanders randomly selected from the New Zealand Electoral Roll.

Thus a total of 3,318 individuals completed questionnaires in Wave 3, including 1,835 from HWR wave 2 and 148 of the HWR wave 1 participants. Ignoring the latter group of re-entering participants, the NZLSA project thus contains a sub-sample of approximately 1,800 New Zealanders who have been comprehensively surveyed three times since 2006 on aspects of their health, wealth and social wellbeing in the transition from later working life to retirement.

The representativeness of the baseline study and the effects of attrition were analysed, and the results are presented in full in Appendix B. Both the HWR baseline sub-samples (Māori and non-Māori) align closely with their respective New Zealand populations, as evident in the proportions of:

• participants across age groups
• men and women
• those in full-time work, and
• 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:

• currently in relationships (partnered)
• in part-time work versus retired/other,
• tertiary-educated, and
• earning above $20,000.

In this regard, as opposed to the corresponding age-matched New Zealand population, the HWR sample in general reflects a disproportionately greater number of New Zealanders who are still working.

Analysis of the effects of attrition suggests that the wave 2 sample consists 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.