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ABSTRACT
Mixed-member proportional electoral systems are characterised by having two types of members of parliament (MPs): district MPs elected directly in a district and list MPs elected via a party list. While it has been suggested that district MPs have a more prestigious and safe position than list MPs, little is known about possible differences between list and district MPs in terms of the length of their parliamentary careers. Using data on all New Zealand parliamentary elections between 1996 and 2017, the authors investigate to what extent the mode in which MPs are elected throughout their careers relates to the length of their careers. The authors’ descriptive and multivariate Cox Proportional-Hazards analyses show that those entering parliament as list MPs have shorter careers than those entering parliament as district MPs. However, when list MPs ‘move on’ to becoming district MPs during their parliamentary career, they have the longest careers of all MPs.
Acknowledgements
The first author graciously acknowledges the financial support of Victoria University of Wellington and the Institute of Mathematical Innovation of the University of Bath. A draft version of the paper has been discussed at a research workshop organised by the Department of Politics, Languages and International Studies (University of Bath). The authors are very thankful for the useful feedback and suggestions. They would also like to thank Fiona Barker, Hamish Clark, Sam Crawley, Chloe Fitz Patrick, Simon Forbes, Kaitlin Martin-Feek and the New Zealand Parliamentary Information Service for their assistance with data collection.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1 The parliament can temporarily expand beyond 120 MPs if a party wins more districts than the number of seats to which it is entitled based on its share of the nationwide vote.
2 These seats overlay the General districts. The number of Māori seats – also referred to as Māori electorates – can vary depending on how many voters of Māori descent choose to enrol on the Māori roll rather than the General roll.
3 For each legislative period, the data records all MPs who entered parliament after the election. It does not take account of changes during the legislative period, such as replacements of MPs who retire or resign. Fifteen MPs took breaks ranging from three to 15 years. They are each counted as one MP.
4 The vast majority of candidates in New Zealand are so-called dual candidates, campaigning both as district and list candidates. Of our sample of elected MPs, 86.3 per cent of all elected district MPs and 80.0 per cent of all elected list MPs (with each seat/list and election year combination taken as one observation) were dual candidates.
5 MPs elected in a Māori seat are defined as district MPs. We ran an additional analysis excluding the Māori seats. Results (see Table S1 in the supplementary material) were similar to those presented later.
6 The confidence intervals for the mixed careers are significantly larger due to these categories having fewer MPs hence making our estimates for average term length more uncertain.
7 To account for the fact that some MPs were already MPs before the first MMP elections held in 1996 (a phenomenon known as left-truncation (Howards et al. Citation2006)), we performed a supplementary analysis with all MPs who were in parliament before 1996 removed. In addition, and to account for the fact that some MPs leave parliament of their own volition, we completed a separate analysis where any MP who did not run in the next election was censored. This allowed us to look at the length of district MPs’ potential career if they were to stay in parliament until they lost an election. The results of both analyses (see Tables S2 and S3 in the supplementary material) were similar to those presented herein.
Additional information
Notes on contributors
Hilde Coffé
Hilde Coffé is a Professor in Politics at the Department of Politics, Languages and International Studies at the University of Bath. Her main research interests include political behaviour, public opinion, political representation, and gender and politics.
Josh Givens
Josh Givens is a PhD student at the Centre for Doctoral Training in Computational Statistics and Data Science (Compass) at the University of Bristol. His PhD project focuses on handling missing data in the field of density ratio estimation. His main research interests include density ratio estimation, missing data, survival analysis, and the statistical analysis of political behaviour and public opinion.
Beate Ehrhardt
Beate Ehrhardt is a Mathematical Innovation Research Associate at the Institute for Mathematical Innovation (IMI) at the University of Bath. Her research focuses on the statistical analysis and application of machine learning to academic research across all faculties of the University of Bath.