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The impact of in-work tax credit for families on self-rated health in adults: a cohort study of 6900 New Zealanders
  1. Frank Pega1,2,
  2. Kristie Carter1,
  3. Ichiro Kawachi2,
  4. Peter Davis3,
  5. Fiona Imlach Gunasekara1,
  6. Olle Lundberg4,5,
  7. Tony Blakely1
  1. 1Health Inequalities Research Program, University of Otago, Wellington, New Zealand
  2. 2Department of Social and Behavioral Sciences, Harvard School of Public Health, Boston, Massachusetts, USA
  3. 3Centre of Methods and Policy Application in the Social Sciences, Department of Sociology, University of Auckland, Auckland, New Zealand
  4. 4Centre for Health Equity Studies, Stockholm University/Karolinska Institutet, Stockholm, Sweden
  5. 5Department of Health Sciences, Mid Sweden University, Östersund, Sweden
  1. Correspondence to Frank Pega, Health Inequalities Research Program, University of Otago, Wellington, PO Box 7343, Wellington, New Zealand, Frank.pega{at}


Background In-work tax credit (IWTC) for families, a welfare-to-work policy intervention, may impact health status by improving income and employment. Most studies estimate that IWTCs in the USA and the UK have no effect on self-rated health (SRH) and several other health outcomes, but these estimates may be biased by confounding. The current study estimates the impact of one such IWTC intervention (called In-Work Tax Credit) on SRH in adults in New Zealand, controlling more fully for confounding.

Methods We used data from seven waves (2002–2009) of the Survey of Family, Income and Employment, restricted to a balanced panel of adults in families. The exposures, eligibility for IWTC and the amount of IWTC a family was eligible for, were derived for each wave by applying government eligibility and entitlement criteria. The outcome, SRH, was collected annually. We used fixed effects regression analyses to eliminate time-invariant confounding and adjusted for measured time-varying confounders.

Results Becoming eligible for IWTC was associated with no detectable change in SRH over the past year (β=0.001, 95% CI −0.022 to 0.023). A $1000 increase in the IWTC amount a family was eligible for increased SRH by 0.003 units (95% CI −0.005 to 0.011).

Conclusions This study found that becoming eligible for IWTC or a substantial increase in the IWTC amount was not associated with any detectable difference in SRH over the short term. Future research should investigate the impact of IWTC on health over the longer term.


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