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Socioeconomic Determinants of Body Mass Index of Adult Chinese in the 1990s Zhehui Luo, Ph.D. MS Department of Epidemiology Michigan State University
Outline • Simple Model • Data and Econometric Issues • Trends and Descriptives • Results of Reduced Form Demand • Results of Dynamic Demand • Results of Production Function
The Model s. t.
The Model • If total time available for leisure and work is not affected by health status • Labor is the same as the effective labor in Grossman’s sense • Equilibrium condition is:
The Data • Chinese Health and Nutrition Survey (CHNS) 1989, 1991, 1993 and 1997 • Carolina Population Center at the University of North Carolina, Institute of Nutrition and Food Hygiene, Chinese Academy of Preventive Medicine • Sampling: multistage, random cluster process
Adults aged 20 and above Excluding pregnant women Sample size: 1989: 4550 persons, 2736 households 1991: 7356 persons, 3402 HH 1993: 6926 persons, 3164 HH 1997: 7580 persons, 3512 HH The Data
The Data • BMI: Weight (kg)/ height (m2)
The Data • Calorie, fat, protein intakes and percent of Calories from fat, protein and carbohydrates • The 1991 China Food Composition Table • 1 gram fat = 9 Kcal energy 1 gram protein = 4 Kcal energy 1 gram carbohydrates=4 Kcal energy
Trends in Food Availability Source: FAO 2002 Food Balance Sheet for China
Trends in overweight and obesity % Men and Women overweight (BMI 25) % Men and Women obese (BMI 30)
% Men overweight by age groups % Women overweight by age groups Trends in overweight
% Men overweight by rural-urban residence % Women overweight by rural-urban residence Trends in overweight
% Men overweight by education levels % Women overweight by education levels Trends in overweight
BMI Distribution: Men Russel Davidson and Jean-Yves Duclos (2000), performed with DAD 4.3
BMI Distribution: Women Russel Davidson and Jean-Yves Duclos (2000), performed with DAD 4.3
Estimating Equation The linear representation: Baltagi and Wu (1999)
Estimating Equation • Econometric Issues • Measurement Errors • Functional form: nonlinearity of effects • Age, cohort and period effects
Age, Period and Cohort Analysis • To identify: • Origin-related process – cohort effect dominant • Aging process • Instantaneous process – function of time • Linear dependency: • Deaton (1997), Holford (1983)
Age, Period and Cohort Analysis • Spacing of the data determines the number of extra constraints (n) needed • CHNS 1989, 1991, 1993, 1997: n=2 • If arbitrarily impose two constraints:
Age, Period and Cohort Analysis • Meaningful constraints: Source: State Statistical Bureau (1992): 1990 Population Census of China.
Age, Period and Cohort Analysis • Results from age dummies, five-year cohort dummies and year dummies:
Reduced Form Demand (I) • Results from the basic model: • Education effect on female BMI inversely U-shaped • % Calories from fat and protein increase with education • Male BMI increases with productive assets, female inversely U-shaped • % Calories from fat and protein increase with assets, except for urban men – U-shaped
Reduced Form Demand (II) • Results from the augmented model: • Prices significant without controlling community dummies in BMI regressions • Negative price elasticity of rice, eggs for calories, fat and protein; positive price elasticity of pork • Better water source – fat, protein intakes and male BMI: positive • More excreta – calories and protein: negative
Dynamic BMI Demand • Estimating Equation: • Instruments: previous years HH resources, community characteristics • Results: • In short terms lagged BMI is good summary measure of health status • Age effect for women still strong, aging factor
BMI Production Function • Estimating equation: • Instruments: previous years HH resources, community characteristics • Results: • In a short period, BMI – a random walk process • Heavy physical activities negative in OLS and positive in IV • Food intakes not significant
Limitations and Future research • Measurement: productive assets, fat intake • Uncertainty • Attrition • Health and Labor Market Participation • Intra-household allocation and Health