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

We would like to understand the rise in obesity in the western (and other) nations.

Why have weights gone up?

Why have weights gone up?

And

Can we explain the puzzle of over-eating and anorexia emerging at the same time?

The idea in the paper

The idea in the paper

People’s utilities may depend, in poorly understood ways, on relative weight.

If so, comparison effects can in principle create ‘obesity spirals’..

.. while those with convex utility get thinner.

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.

First: some background.

Economics is changing

Researchers are studying mental well-being.

We are drawing closer to psychology and medicine.

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.

Consider weight and well-being.

In work on BHPS with Nick Powdthavee

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.

So again…

then why have people’s weights risen?

• 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

Thinking how imitation could work

Thinking how imitation could work

Using proxy utility data, say, could we show that..?

Happiness = f(BMI relative to others’ BMI, controls)

If so, and utility is concave in relative position, it is rational for people to emulate each other.

A general point about the mathematics of imitation

A general point about the mathematics of imitation

Caring about relative things is not sufficient to give us Keeping up with the Joneses.

What matters is the sign of the second derivative of the utility function with respect to status.

Concavity leads to imitation.

Convexity produces deviance.

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.

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 )()(

Empirically, is utility convex or concave in status?

Empirically, is utility convex or concave in status?

Not easy to know.

Wimbledon case evocative.

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

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)

A natural question

How do people perceive themselves?

A natural question

How do people perceive themselves?

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?”

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

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.

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

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

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

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

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.

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

Is there longitudinal evidence?

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.

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

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

Others’ weight affects well-being

Summing up

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.

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.

Time for lunch?

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