title: The impact of in-work tax credit for families on self-rated health in adults: a cohort study of 6900 New Zealanders.
abstract: 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.
authors.affiliation: Health Inequalities Research Program, University of Otago, Wellington, New Zealand. Frank.pega@otago.ac.nz
authors.forename: Frank
authors.initials: F
authors.lastname: Pega
authors.forename: Kristie
authors.initials: K
authors.lastname: Carter
authors.forename: Ichiro
authors.initials: I
authors.lastname: Kawachi
authors.forename: Peter
authors.initials: P
authors.lastname: Davis
authors.forename: Fiona Imlach
authors.initials: FI
authors.lastname: Gunasekara
authors.forename: Olle
authors.initials: O
authors.lastname: Lundberg
authors.forename: Tony
authors.initials: T
authors.lastname: Blakely
mesh_terms: D000328:Adult; D004608:Eligibility Determination; D004651:Employment; D005260:Female; D006304:Health Status; D006801:Humans; D007182:Income / Q000706:statistics & numerical data*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009520:New Zealand; D011203:Poverty / Q000706:statistics & numerical data; D012044:Regression Analysis; D012946:Social Welfare; D013660:Taxes; D055815:Young Adult
keywords: EMPLOYMENT; LONGITUDINAL STUDIES; POLICY; POVERTY; SELF-RATED HEALTH