#HEJC for 26/02/2015

The next #HEJC discussion will take place Thursday 26th February, at 11pm London time on Twitter. To see what this means for your time zone visit Time.is or join the Facebook event. For more information about the Health Economics Journal Club and how to take part, click here.

The paper for discussion is a working paper published by the Canadian Centre for Health Economics (CCHE). The authors are Koffi-Ahoto Kpelitse, Rose Anne Devlin and Sisira Sarma. The title of the paper is:

The effect of income on obesity among Canadian adults

Following the meeting, a transcript of the Twitter discussion can be downloaded here.

Links to the article

Direct: http://www.canadiancentreforhealtheconomics.ca/wp-content/uploads/2014/08/Sisira-et-al.pdf

RePEc: https://ideas.repec.org/p/cch/wpaper/14c002.html

Summary of the paper

This is the first paper to examine the causal relationship between income and obesity in the Canadian context. To do so, they examined data from five biennial Canadian Community Health Survey (from 2000/01 to 2009/10), a nationally representative survey collecting information on over 100,000 individuals each survey.

Initially, the paper explored the Grossman model, which suggested increasing income would promote healthy lifestyle investments, and thus lead to a negative relationship between income and obesity. Previous studies that examined this link were discussed, some (eg. Lindahl (2005)) demonstrating a negative relationship; some (eg. Schmeiser (2009)) demonstrating a positive relationship; some (eg. Cawley (2010)) finding no evidence of a causal relationship.

Additionally, education and employment were explored. Again, the Grossman model was used as a basis, predicting i) a negative relationship between education level and obesity with a greater income effect amongst educated people and ii) a negative relationship between employment level and obesity. However, regarding education, prior studies discussed have shown “mixed results”, and regarding employment, the authors were not aware of any study to examine this causal relationship, but suggested the relationship was ambiguous.

Finally, the relationship between gender and obesity were discussed. Numerous studies have shown negative association between income and BMI amongst women, but for men, the relationship is unclear (some showing positive relationship, some negative, and some no significant relationship at all). The importance of the effect of obesity on labour market outcomes (outlining the “large” empirical literature showing obese women more likely to suffer discrimination in the labour market) was outlined.

In this study, the authors found that:

  • From 2000/01 to 2009/10, BMI and obesity rates amongst both men and women have risen.
    • For men, the obesity rate rises from 19.48% for those with income below $10k to 26.09% for those with income over $80k.
    • For women obesity falls from 26.71% for those below $10k to 17.38% for those with income over $80k.
  • For men, a 1% rise in household income leads to 0.027 point decrease in BMI (2SLS estimate); 0.084kg reduction and 0.27% point decrease in probability of being obese (linear IV procedure).
  • For women, a 1% rise in household income leads to 0.113 point decrease in BMI (much higher than for men; this used a 2SLS estimate); 0.300kg reduction; and 0.76% point decrease in probability of being obese (linear IV procedure).
  • For men the effect of income on BMI was only demonstrated at higher BMI distribution, while for women the effect of income on BMI was found throughout with a larger effect at higher BMI.
  • Education had a variable relationship amongst both men and women, not consistent with the theoretical prediction that the effect would be larger amongst educated people.
  • The effect of employment for men was mixed, with a negative effect of income on BMI only in employed men and a negative effect of income on obesity probability only in unemployed men.
  • The effect of employment for women was more consistent with theoretical predictions, showing negative effects of income on both BMI and on the probability of being obese across employment status.
  • Higher BMI and probability of obesity was associated with older age, marriage (much greater effect in women), household size (much greater effect in women) and home ownership.
  • Lower BMI and probability of obesity was associated with being widowed/separated/divorced, being an immigrant and living in urban area (in men).

In summary, this study supports the findings of Lindahl, and stands in contrast to Schmeiser, Cawley and other related studies.

Discussion points

  • Why might there be significant variation in findings between the different studies discussed?
  • Are there ways in which unemployment and neighbourhood income might directly influence BMI?
  • Is the set of control variables used in the authors’ models satisfactory?
  • Is it of concern that policies to increase household income could be regarded a pure, explicit public health policy?
  • Are there relevant studies from other countries?
  • To what extent are these findings generalisable?

Can’t join in with the Twitter discussion? Add your thoughts on the paper in the comments below.