imitative obesity eea conference in milan sunday 31 august 2008
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Imitative Obesity EEA Conference in Milan Sunday 31 August 2008. David G. Blanchflower Dartmouth College; Bank of England; and NBER Andrew J. Oswald University of Warwick Bert Van Landeghem University of Leuven. - PowerPoint PPT PresentationTRANSCRIPT
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Imitative ObesityImitative Obesity
EEA Conference in MilanEEA Conference in Milan
Sunday 31 August 2008Sunday 31 August 2008
David G. BlanchflowerDavid G. BlanchflowerDartmouth College; Bank of England; and NBERDartmouth College; Bank of England; and NBER
Andrew J. OswaldAndrew J. OswaldUniversity of WarwickUniversity of Warwick
Bert Van LandeghemBert Van LandeghemUniversity of LeuvenUniversity of Leuven
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We would like to understand the rise in obesity in the western (and other) nations.
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Why have weights gone up?
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Why have weights gone up?
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And
Can we explain the puzzle of over-eating and anorexia emerging at the same time?
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The idea in the paper
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The idea in the paper
People’s utilities may depend, in poorly understood ways, on relative weight.
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If so, comparison effects can in principle create ‘obesity spirals’..
.. while those with convex utility get thinner.
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In the data, we find:
• perceptions do depend on others’ BMI
• dieting is correlated with relative weight
• some evidence that others’ weights affect life-satisfaction.
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First: some background.
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Economics is changing
Researchers are studying mental well-being.
We are drawing closer to psychology and medicine.
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There is evidence in Britain, the Netherlands and Belgium that mental strain is increasing.
• Verhaak, P.F.M., Hoeymans, N. and Westert, G.P. (2005). ‘Mental health in the Dutch population and in general practice: 1987-2001’, British Journal of General Practice, vol. 55, pp.770-775.
• Hodiamont, P.P.G., Rijnders, C.A.T., Mulder, J. and Furer, J.W. (2005). ‘Psychiatric disorders in a Dutch Health Area: a repeated cross-sectional survey.’ Journal of Affective Disorders, vol. 84, pp.77-83.
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Consider weight and well-being.
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In work on BHPS with Nick Powdthavee
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In work on BHPS with Nick Powdthavee
.. we find that BMI enters negatively in regressions for
Life satisfactionHappinessWell-being measured by GHQ
Oswald-Powdthavee “Obesity, Unhappiness and the Challenge of Affluence: Theory and Evidence”, Economic Journal, 2007.
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So again…
then why have people’s weights risen?
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• Christakis, N. A. and J. H. Fowler "The spread of obesity in a large social network over 32 years." New England Journal of Medicine, 2007.
• Clark, A.E. and A.J. Oswald "Comparison-concave utility and following behaviour in social and economic settings", Journal of Public Economics, 1998
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Thinking how imitation could work
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Thinking how imitation could work
Using proxy utility data, say, could we show that..?
Happiness = f(BMI relative to others’ BMI, controls)
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If so, and utility is concave in relative position, it is rational for people to emulate each other.
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A general point about the mathematics of imitation
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A general point about the mathematics of imitation
Caring about relative things is not sufficient to give us Keeping up with the Joneses.
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What matters is the sign of the second derivative of the utility function with respect to status.
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Concavity leads to imitation.
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Convexity produces deviance.
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A general point about the mathematics of imitation
Say a person is choosing an action a to solve:
Maximize v(a – a*) – c(a)
where a* is what everyone else is doing.
But then if v(.) is concave (convex) in status, it is rational to act similarly to (deviantly from) the herd.
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Status may come from rank
• Assume the person rationally chooses body weight. He or she picks b to maximize
s.t.
where r is ordinal rank in the slimness distribution in society, v(r) is the utility from that rank, u(b) is the direct benefit from high body weight, and a constant c is the marginal cost of body weight.
cbbrvbuV ))(()(
b
b
dxxfbr )()(
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Empirically, is utility convex or concave in status?
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Empirically, is utility convex or concave in status?
Not easy to know.
Wimbledon case evocative.
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DataData
• Eurobarometers #64.3 (2005) – 29 countries. EU-27 + Croatia + Turkey
• Eurobarometer #44.3 (1996) – 15 EU countries
• Health Survey of England, 2004
• British Cohort Study, 2004/5 sweep
• National Child Development Study, 2004/5
• German Socio-Economic Panel, 2002, 2004 & 2006
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Table 1. Self-reported BMI by country Table 1. Self-reported BMI by country
• BMI=kilos/ height in metres squared
• Highest for men and women in Malta
• Lowest for men in Latvia and Turkey (24.8)
• Lowest for women in Italy (23.5)
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A natural question
How do people perceive themselves?
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A natural question
How do people perceive themselves?
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Table 2. Feeling overweight Table 2. Feeling overweight
• Individuals in Eurobarometer #64.3 survey are also asked
• “Would you say that your current weight is: Too low; About right; Too high?”
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Table 2. Feeling overweight Table 2. Feeling overweight
• Individuals in Eurobarometer #64.3 survey are also asked
• “Would you say that your current weight is: Too low; About right; Too high?”
• 31% of male Europeans, and 43% of female Europeans, say their own weight is too high
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Table 3. Feeling overweight: relative BMITable 3. Feeling overweight: relative BMI • Relative BMI = BMI divided by the
average BMI from their country*age band*gender cell.
• Age bands are defined in twelve five year age groupings from <20; 20-24 and so on in five year bands up to 69 and then 70 and over.
• Regardless of absolute BMI, those reporting fatness relative to their peers are more concerned about their own weight. Relative weight matters.
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Table 3. Feeling Table 3. Feeling overweightoverweight - ordered logit - ordered logit
All Male Female
BMI .7734 1.0494 .9869
BMI2 -.0074 -.0080 -.0111
Relative BMI 3.7325 -1.7354* 2.6194
N 27,092 12,199 14,893
* Coefficient insignificantly different from zero
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Table 3. Feeling overweight - ordered logit Table 3. Feeling overweight - ordered logit
• Decreasing effect in age, particularly for women.
• The most highly educated Europeans are more likely to view themselves as overweight
• BMI enters with an inverted U-shape with a turning point around 50
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Table 4. Table 4. DisDissatisfaction with weight and dieting - satisfaction with weight and dieting - 19961996
• Here are some statements. For each of these, please tell me if you agree strongly, agree slightly, disagree slightly or disagree strongly?
1) I am very satisfied with my body weight. Agree strongly=1 … disagree strongly=5
2) Over the last 12 months, have you been on a diet, or not?
• 24% of women and 13% of men had been on a diet
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Table 5. Table 5. DisDissatisfaction with weight - ordered logitsatisfaction with weight - ordered logit
Male Female
BMI .2387* .6065
BMI2 .0005* -.0072
Relative BMI -.7220* 1.2250
N 7,245 7035
* Coefficient insignificantly different from zero
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Table 5. Table 5. DisDissatisfaction with weight – relative BMIsatisfaction with weight – relative BMI
• Among Europe’s females, a high value of relative BMI is a predictor of those who say they are dissatisfied
• Highly educated people are more likely, ceteris paribus, to be dissatisfied with their weight.
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Table 5. Recently been on a diet - dprobitTable 5. Recently been on a diet - dprobit
Male Female
BMI .0176 .0239
BMI2 -.0001 -.0004
Relative BMI .1595 .6001
N 7,251 7,045
* Coefficient insignificantly different from zero
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Is there longitudinal evidence?
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German Socio-Economic PanelGerman Socio-Economic Panel
• The GSOEP is a representative longitudinal study of private households.
• The panel was started in 1984. In June 1990 the GSOEP was extended to the GDR.
• There are 20,229 observations for 2002, 18,913 for 2004 and 20,704 for 2006.
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Fixed effect models using GSOEPFixed effect models using GSOEP
• Table 8 gives non-linear impact of BMI using OLS
• Inverted U-shape in BMI
• Also present in the fixed effects
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Fixed effect models using GSOEP – relative BMIFixed effect models using GSOEP – relative BMI
• Table 9 includes log of BMI
• It also includes log of the average BMI by 16 federal states and 3 year cells
• Log BMI in the fixed effects is insignificant for women and positive for men
• The coefficient on Log Average BMI is significant for men. The result implies that, after differencing out person-effects, life satisfaction is higher among those men who live in an area populated by fatter individuals
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Others’ weight affects well-being
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Summing up
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Conclusions - 1Conclusions - 1
• It may be that people’s utility functions contain relative BMI.
• If so, this is consistent, under certain conditions, with the idea of obesity imitation or contagion.
• One third of Europe’s population think of themselves as overweight.
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Conclusions - 2Conclusions - 2
• There is a negative relationship between BMI and happiness in cross-sections.
• For German males, in a fixed-effects framework, life satisfaction is greater among those who live in places where other people tend to be fatter.
• Consistent with Christakis and Fowler, weight comparisons seem to matter.
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Imitative ObesityImitative Obesity
EEA Conference in MilanEEA Conference in Milan
Sunday 31 August 2008Sunday 31 August 2008
David G. BlanchflowerDavid G. BlanchflowerDartmouth College; Bank of England; and NBERDartmouth College; Bank of England; and NBER
Andrew J. OswaldAndrew J. OswaldUniversity of WarwickUniversity of Warwick
Bert Van LandeghemBert Van LandeghemUniversity of LeuvenUniversity of Leuven