3.2  The New Zealand Election Study data

Intergenerational mobility was also measured using occupation data from the large nationwide 1996 New Zealand Election Study (NZES) dataset.[14] In 1996, the NZES's post-election survey asked respondents what their occupation was and what their parents' occupations had been when the respondent was aged about 14. It was not until 2008 that the Election Study again asked respondents about their parents' occupations, and the 2008 data is not yet available. Researchers in other countries have also used election study data to study intergenerational mobility (Heath and Payne, 1999, p. 4), and similar questions from household economic surveys (Ermisch, et al., 2006, p. 663).

The NZES's sample frame was people on the electoral roll. In 1996, 91.6% of eligible voters were enrolled and 88% of enrolled electors voted (New Zealand Post, 1997, section 80). The Election Study’s postal response rate was 55.7% (4,118 respondents), which is high by international standards. Groups that are less likely to be on the electoral roll, vote and answer surveys include those who move frequently, young people, people who are travelling overseas, Māori and some ethnic groups (Electoral Enrolment Centre, [2008], p. 10; Electoral Law Committee, 1998, pp. 26-33; Jackson, 1996, p. 14; Vowles, 2002b, pp. 99-103). The Election Study weight ensures that the data matches voting behaviour, but the data does not always perfectly mirror the characteristics of New Zealand’s population. As a result, caution is necessary when interpreting the results.

The Election Study had a large sample size and deliberately sampled a higher proportion of people who had chosen to be on the Māori electoral roll than on the general electoral roll. Nevertheless, only 13.5% of the Election Study's weighted sample of mail respondents identified as Māori (solely or in part), compared to 14.5% of New Zealanders in the 1996 census (Statistics New Zealand, 1998a). Because there are 374 cases where we have both the respondent’s occupation and that of their father[15] we are able to cautiously study intergenerational mobility by Māori. With only 31 such cases for Pacific peoples we are unable to calculate intergenerational mobility by them. In total, 15.7% of the Election Study's mail respondents were born outside New Zealand compared to 17.5% of New Zealand's population (Statistics New Zealand, 1998c). Apart from sampling a higher proportion of voters on the Māori roll, the Election Study sample is a simple random sample.

Of the Election Study mail sample, we were able to include 79.8% of total cases in our regressions (3,256 cases) and 67.7% of Māori respondents (374 cases). The single biggest reason why we lose cases is because respondents were economically inactive. A detailed analysis of why we lose cases is included in Section 8.2.

People's occupation determined their Socio-Economic Status (SES) score on the 10 to 90 scale. The average income of people in different occupations in the 1996 census, together with data on their educational qualifications and survey data on the value of goods they consumed, calculated the SES of occupations (Davis, Jenkin and Coope, 2003, pp. 12-16). On average, people in higher SES occupations, such as corporate managers and general practitioners, have higher incomes and educational qualifications than people in lower SES occupations, such as labourers and textile workers. Since occupation is an excellent indicator of permanent income (the average income that an individual expects to receive over their life-time), intergenerational mobility has frequently been calculated using SES data (Blanden, 2008, pp. 6, 16; Corak, 2006, p. 8; Ermisch, et al., 2006, pp. 674, 677). While people’s SES is not the same as their income, the SES scores are correlated with health and economic outcomes (Davis, et al., 2003, p. 11).[16]

Our data on people's SES has a number of limitations. Some of the SES groups, and farming in particular, contain people from a wide range of economic circumstances. This variation is only partly caused by life-cycle effects (Davis, et al., 2003, pp. 12, 27). Farming is an important part of the New Zealand economy and 16.7% of Election Study respondents listed their father’s occupation as being a farm or animal producer or farm worker. The inability of our data to measure the different economic circumstances of people from a farming background is therefore an important limitation. Another limitation is that the SES of occupations can gradually change over time as relative pay rates and educational requirements change. In addition, we are relying on people’s recall of their father’s occupation. This recall may be inaccurate, particularly when their father had a number of jobs. Indeed, people may sometimes “uplift” their occupational status and that of their parents to present themselves and their parents in the best possible light (Atkinson and Harr, 1978, pp. 62-64; Galt, 1985, pp. 89, 124). The Election Study data is now over 14 years old, and there have been changes to New Zealand’s workforce since 1996. Because the occupational careers of women are sometimes quite complex, since they frequently spend time outside the workforce looking after children, we have followed overseas studies in only using data on the occupation of people’s fathers (Ermisch, et al., 2006, p. 664; Ganzeboom and Treiman, 2007, p. 17).