REVISITING THE SOCIOECONOMIC GRADIENT IN OBESITYLooking Beyond the Obesity Threshold

Inaugural Conference of the Singapore Health Economics Association

Marcel Bilger1, Eliza Kruger1, Eric Finkelstein1, 2

1 Signature Program in Health Services & Systems Research Duke-NUS Graduate Medical School, Singapore 2 Lien Centre for Palliative Care, Duke-NUS, Singapore

April 17th, 2013

Outline

Why study socioeconomic inequality in obesity

Our proposed method to measure socioeconomic inequality

Trends in socioeconomic inequality in obesity in the US

Decomposition of socioeconomic inequality according to gender, race and other factors

Discussion

Obesity Rates

One of the most prominent health concerns facing the US is the growing prevalence of obesity

Rates for adults have more than doubled in the past 30 years (CDC 2010) 66% of adults are overweight 34% are obese

Singapore is also affected as obesity rates have increased from 6% in 1998 to 11% in 2010 (MOH Singapore)

Distribution of Obesity

Whether the rich or the poor are disproportionally affected by obesity matters too

If the poor are disproportionally affected: This will contribute to increase health

inequality The poor will not be able to financially cope

with the increased health risks they face Ultimately, this will affect the public health

care sector, through increased subsidies and/or increased social insurance premiums

Concentration Index (CI)

Measures degree of socioeconomic inequality in health (e.g. obesity)

CI<0: the poor are more affected by obesity

CI>0: the rich are more affected by obesity

CI is normalized between -1 and +1

Source: Zhang Q, Wang Y (2007)

Foster-Greer-Thorbecke (FGT) measures

c is the obesity threshold (i.e. BMI>30) α is the parameter that sets the sensitivity

of the measure above the threshold α = 0: Y measures obesity status α = 1: Y measures depth of obesity α = 2: Y measures severity of obesity

𝑌={(𝐵𝑀𝐼− c)∝ 𝑖𝑓 𝐵𝑀𝐼≥ c0 otherwise

Data

National Health and Nutrition Examination Survey (NHANES)

Inclusion criteria – age 20 to 65, non-pregnant, data on income and BMI available

We separately analyze data from 5 time periods (sample size in brackets); NHANES 1 1971-1974 (2,986) NHANES 2 1976-1980 (9,101) NHANES 3 1988-1994 (12,275) Continuous NHANES 1999-2004 (8,533) Continuous NHANES 2005-2010 (7,969)

Variable Definitions

Poverty income ratio calculated by dividing family income by the

poverty lines established by the federal Register Education (5 levels) Gender Race (Mexican American, Non-Hispanic White,

Non-Hispanic Black) Immigration status (born outside the US or

not) Marital status (5 levels)

Concentration Index of Status, Depth and Severity of Obesity (BMI>30)

Decomposition of Overall Socioeconomic Inequality in Obesity (2005-2010)

Decomposition of the CI by race

Decomposition of the CI by Gender

Summary

• We propose measures of socioeconomic inequality in obesity that account for excess weight above the obesity threshold

• In the US, there is no socioeconomic inequality in the prevalence of obesity anymore

• But the poor are still disproportionally more severely obese than the rich

• Socioeconomic inequality in obesity greatly varies according to race, gender, and many other factors

• Decomposition analysis permits finer analysis

Discussion• Poor obese individuals will not be able to

financially cope with the consequences of their increased health risks

• Socioeconomic inequality thus increases the burden on the public health sector

• Given the increase in obesity prevalence in Singapore, a similar analysis would be useful

• The measures we propose are not limited to obesity but could be applied to any quantitative variables with a threshold or ceiling– e.g. hypertension, diabetes