Ewan Gray University of Aberdeen Health Economics Research Unit (HERU) Time Preferences and the Development of Obesity

Time Preferences

Time Perspective Time Perspective is an equivalent psychological concept. Consideration of Future Consequences Scale (CFCS) is a survey instrument designed to measure time perspective/time preference. High correlation with time preference rate.

CFCS Examples (1-7 scale): –“I am only concerned about the present, because I trust that things will work themselves out in the future.” –“With everything I do, I am only concerned about the immediate consequences (say a period of a couple of days or weeks). ”

Incredibly simple model Other factors influencing intentions Time Preferences Intentions Health Behaviours

DHS DnB Household Survey (DHS) –Data from Use –2,000 (1660 by 2009) households on CentERpanel (representative of Netherlands population). Online, arrangements for access with no computer. Self-report. –Includes: Basic demographic, basic health (BMI, limiting health problem, smoking, alcohol consumption), detailed income, assets, liabilities and some interesting psychological variables (time preferences, risk preferences, personality). –Includes CFCS, height and weight. –Previous cross-sectional study found weak evidence of association of high TP and increased BMI (Borghans and Golsteyn, 2006).

Aim Do time preferences (CFCS score) effect the development of obesity? Previous studies have not obtained a conclusive answer. –Five previous studies (4 cross-sectional, 1 ecological) have found mixed evidence of a weak effect of time preference. –Statistical significance only achieved for sub-groups or in some models in each cross-sectional study. Studies used moderately large data-sets from USA, Netherlands, England and Japan.

Methods Non-parametric –Plot Kaplan-Meier survival functions for quartiles of CFCS distribution. Log-rank test. Semi-parametric –Cox regression –CFCS score is independent. –Controlling for age, gender, education and initial BMI. –

Results Log-rank test: χ 2 = 14.16, p

Results 2 VariableModel 12 – Quadratic Age3 – Interactions CFCS0.01**(0.004)0.011**(0.004)0.011*** (0.004) Age-0.01***(0.003)0.061***(0.018)0.067***(0.018) Gender (Male)-0.386***(0.067)-0.385***(0.075)-1.474***(0.289) University-1.18***(0.225)-1.104***(0.226)-1.113***(0.226) U. Secondary-0.544***(0.097)-0.486***(0.096)-0.502***(0.099) Age ***(0.0002) ***(0.0002) Gender*Age0.023***(0.006) Coef. (s.e.), *P<0.1, **P<0.05, ***P<0.01

Results 3 Variable5- InitialBMI CFCS0.015***(0.004) Age0.063***(0.022) Gender (Male)-0.221(0.333) University0.369(0.284) U. Secondary0.346***(0.126) Age ***(0.0002) Gender*Age0.003(0.006) Initial BMI0.288***(0.006)

Sensitivity to Obesity BMI cut-off value

Conclusions CFCS is significantly associated with hazard of obesity. A high CFCS predicts greater hazard of obesity. Hazard ratio (for normalised CFCS): (1.07, 1.238). This estimate is robust to different specifications of the control variables.

Challenges/Limitations Data: –Attrition/censoring is high and may be non-random –Missing and implausible values Models: –Other BMI dynamics than occurrence of BMI>30 are of interest. –Other response variables may be more appropriate such as BMI or a binary dependent with a probit or logit link function.

Questions?

Summary Statistics Variable1996 Mean (s.d.) or %2009 Mean (s.d.) or % Age47.0(14.2)54.9(14.4) Female46.3%44.4% BMI24.3(3.46)26.0(3.99) CFCS score41.63 (11.1)42.95 (8.17) University Education (2002)2.0%8.89% U. Secondary Education (2002) 7.9%26.9%