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  • 1. SNAP and Diet Quality: A Treatment Effects ApproachChristian A. Gregory* Shelly Ver Ploeg Margaret Andrews Alisha Coleman-Jensen Economic Research Service, USDA *contact author: cgregory@ers.usda.gov. Annual Meetings AAEA Seattle, WA August 13, 2012 The views expressed are those of the authors and should not be attributed to ERS or USDA.
  • 2. Background & Motivation Background: Intent of Program• SNAP authorizing legislation: “To alleviate such hunger and malnutrition, a supplemental nutrition assistance program is herein authorized which will permit low-income households to obtain a more nutritious diet through normal channels of trade by increasing purchasing power ...”• food security and nutrition declared goals of SNAPGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 3. Background & Motivation Background: Public Perceptions• “As I look at what this card is paying for in the orders being scanned at the register, I see T-bone steaks, thick-cut sirloins, thick-cut pork chops (all expensive cuts of meat). I see crab legs, bags of shrimp, and box after box of pastries, cakes and doughnuts from the bakery department, and bagged candy, chips and cookies from the snack aisles. Then come the sodas, energy drinks and Starbucks coffee drinks... The people using this card are eating better than most families that have two incomes.” -Letter to Frederick News PostGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 4. Background & Motivation Background: SNAP & Food Security• recent research: SNAP ⇓ food insecurity• Yen et al. (2008); DePolt et al. (2009); Shaefer and Gutierrez (2012); Nord and Golla (2009); Nord and Prell (2011); Ratcliffe et al. (2011)• estimates suggest SNAP participation ⇓ food insecurity 33 - 40 percentGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 5. Background & Motivation Background: SNAP & Diet Quality• recently–a good deal of concern• many expensive chronic illnesses associated with low-income populations• public bears sizable fraction of cost• policy suggestions: – restrict foods eligible for SNAP (as in WIC) – Wholesome Wave Double Coupon – Healthy Incentives PilotGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 6. Background & Motivation Motivation• large extant literature (detail below)• some–improved intakes (Devaney and Moffitt, 1991; Wilde et al., 1999)• some–poorer intakes (Butler and Raymond, 1996; Yen, 2010)• difficult to identify treatment effects selection on unobservables• selection: adverse or beneficial?Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 7. Background & Motivation Our Contribution• use individual data (NHANES) matched to state-level data identify SNAP selection• estimate treatment effects by isolating unobservables in SNAP and diet• show that marginal effect of SNAP is positive and significant for some HEI components; adverse selection accounts for worse diet outcomesGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 8. Background & Motivation Preview of Results• as measured by HEI total and component scores – SNAP participants comparable diets – average treatment effect of SNAP (ATE): slightly lower HEI scores – economically significant? – selection is adverse for many components – effect of SNAP on marginal participant is positive – in particular, SNAP gets participants to consume some whole fruit and whole grains• results corroborated by nutrient intakes• robust to specification choice?• suggest policy caution: tradeoff improving nutritional quality, changing selection into the programGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 9. Previous Research Previous Research• comprehensive review of literature (Fox et al., 2004)• wrt intakes, few find significant impact ↑, ↓• highlight Gleason et al. (2000)–array of outcomes including HEI–rule out large effects in either direction• studies that find positive effects: Wilde et al. (1999); Kramer-LeBlanc et al. (1997); Basiotis et al. (1998)• more recent studies: Cole and Fox (2008); Yen (2010)• Waehrer and Deb (2012) used latent factor model/IV–SNAP participants ↑ caloric sweetened beverages ↓ fruits/vegetablesGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 10. Data Data: NHANES 2003-08• individual: NHANES 2003-04, 2005-06, 2007-08• dependent variable: Healthy Eating Index Score (HEI) (day 1), total and component – total = sum of 12 elements – total fruit, whole fruit, total veg, dark green and orange veg, total grains, whole grains, milk, meat and beans, oils, sat fat, sodium, SoFAAS – for food groups and oils: zero intake = score of zero; meet/exceed dietary recommendation = perfect score; linear interpolation b/wGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 11. Data Data: NHANES 2003-08 (cont)• dependent variable: Healthy Eating Index Score (HEI) (day 1), total and component (continued)• how to score “moderation” components? (i.e. things you should eat less of) – 85th pctile of consumption = score of zero; meet Dietary Guidelines recommendation = score of 8; meet somewhat higher standard, below dietary rec = score of 10; linear interpellation b/w amounts at 0 and 8, 8 and 10. – example: sat fat. – fraction of total energy (2001-2002 NHANES data) • 85th pctile: 15 % : score of 0 • DG: less than 10 %: score of 8 • below 7% : score of 10 – weights: milk, meat/beans, oils, sat fat, sodium = 10; total fruit, whole fruit, total veg, dark green and orange veg, total grains, whole grains =5 ; SoFAAS = 20Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 12. Data Data: NHANES 2003-08• independent variable of interest: HH SNAP participation – 2003, 2005 waves: 2 questions HH SNAP participation: number of persons authorized to receive SNAP, whether HH receive SNAP 12 mos. – 2007 wave: HH receive SNAP 12 mos – we use whether HH receive SNAP 12 mos 2003, 2005, 2007 – robustness check: sample person currently receiving SNAP• other rhs variables: race/ethnicity, income, education, SR weight 1 year ago, age, marital status, employment status, vigorous ex./week, nutrition ed per poor person, hh size, state fixed-effects• 200% FPLGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 13. Data Data: SNAP Policy Database• in model (following) we need exogenous variables to identify participation in SNAP – state-month level variation in three policies: – expanded categorical eligibility–relaxed asset and/or income requirements – biometric info needed to enroll–usually a fingerprint – certification period–median certification period for households with earnings calculated from the QC data• valid: the policies affect SNAP participation but not diet quality/HEIGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 14. Methods Selection Model• one might begin with HEIi = Xi β + SNAPi δOLS + ϵi (1)• problem: SNAP is endogenous to HEI• another way to proceed HEIi = Xi β + SNAPi δZ + ϵi (2) SNAPi∗ = Zi γ + Xi θ + υi (3)• Z exogenous variables for SNAP• SNAP ∗ latent index of SNAP participation• X other variables correlated w/ SNAP, HEI• ϵ and υ bivariate normal w/covariance matrix [ ] σ 2 ρσ V = ρσ 1Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 15. Methods Identification & Marginal Effects• model is theoretically identified by functional form imposed by distribution of ϵ and υ.• we use exogenous policy variables to identify SNAP participation• ATE of SNAP : [ ] ϕ(Zi γ + Xi θ) µi = δZ + ρσ (4) Φ(Zi γ + Xi θ) ∗ [1 − Φ(Zi γ + Xi θ)] this is what δOLS will estimateGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 16. Methods Identification & Marginal Effects• without selection: µi = δOLS ; with selection δZ + difference in expected value of errors conditional on participation (See Greene, 2011)• unconditional on selection, δZ measures marginal affects of SNAP on participants• standard errors (of total effects) (ν) by delta method: let α = [γ, θ] √ ∂µ ∂µ ′ νµ = M , (5) ∂α ∂α where M is the covariance matrix of the selection equationGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 17. Results Descriptive HEI Score and SNAP Participation Data: NHANES, 2003−08 53 51.8 52 51 HEI Score 49 50 47.8 No SNAP SNAP Participants SNAP Participation Status Figure : Differences in HEI over SNAP ParticipationGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 18. Results Descriptive Total Food Energy and SNAP Participation 2044 2074 2104 2134 Data: NHANES, 2003−08 2124.3 2094 Total Energy Intake No SNAP SNAP Participants SNAP Participation Status Figure : Differences in Energy over SNAP ParticipationGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 19. Results Descriptive Table : Means of HEI Components by SNAP Participation HEI Component No SNAP SNAP Difference TotalFruit 2.11 1.73 -0.38*** (0.07) (0.07) (0.12) WholeFruit 1.93 1.39 -0.54*** (0.06) (0.06) (0.10) TotalVeg 3.00 2.63 -0.37*** (0.04) (0.07) (0.08) DkGOrVeg 1.17 0.83 -0.34*** (0.05) (0.05) (0.08) TotGrain 4.27 4.07 -0.20*** (0.03) (0.04) (0.06) WholeGrain 0.93 0.66 -0.27*** (0.04) (0.03) (0.05) N 5,105Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 20. Results Descriptive Table : Means of HEI Components by SNAP Participation, cont’d HEI Component No SNAP SNAP Difference Milk 4.77 4.39 -0.38** (0.09) (0.11) (0.15) Sodium 4.12 4.52 0.40*** (0.07) (0.09) (0.11) SoFAAS 9.47 7.96 -1.51*** (0.20) (0.25) (0.41) N 5,105Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 21. Results ATE of SNAP Table : ATE of SNAP on HEI/Components: 200% FPL HEI TotalFruit WholeFruit TotalVeg DkGOrVegµ -1.241*** -0.144*** -0.520*** -0.069*** -0.103***νµ (0.049) (0.016) (0.082) (0.009) (0.005) TotGrain WholeGrain Milk MeatBeans Oilsµ -0.094*** -0.307*** 0.004 -0.340*** 0.039**νµ (0.005) (0.078) (0.004) (0.000) (0.017) SatFat Sodium SoFAASµ 0.0290*** 0.376*** -0.388***νµ (0.009) (0.001) (0.039)N 5,105Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 22. Results Correlation, IV Strength Table : Selection Paramter: ρ HEI TotalFruit WholeFruit TotalVeg DkGOrVeg ρ 0.082 -0.107 -0.648*** 0.071 0.040 νρ (0.169) (0.223) (0.203) (0.129) (0.301) TotGrain WholeGrain Milk MeatBeans Oils ρ -0.059 -1.032*** -0.017 -0.000 0.066 νρ (0.048) (0.069) (0.096) (0.084) (0.106) SatFat Sodium SoFAAS ρ -0.035 0.003 0.082 νρ (0.127) (0.117) (0.169)• All F-tests of instruments > 15.Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 23. Results Marginal Effects of SNAP Table : Marginal Effects of SNAP=δZ HEI TotalFruit WholeFruit TotalVeg DkGOrVeg δ -1.429 0.270 1.981*** -0.301 -0.236 νδ (1.916) (0.757) (0.624) (0.382) (0.870) TotGrain WholeGrain Milk MeatBeans Oils δ 0.041 1.940*** 0.116 -0.338 -0.425 νδ (0.133) (0.095) (0.598) (0.392) (0.697) SatFat Sodium SoFAAS δ 0.273 0.357 -1.429 νδ (0.908) (0.670) (1.916) N 5,105Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 24. Results Questions• δs seem too large to be believed• δwf = 1.98, x = 1.39 ¯• δwg = 1.94, x = .66 ¯Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 25. Results Distribution of Components Kernel Density WholeFruit Component Score Kernel Density WholeGrain Component Score Data: NHANES 2003−08, 200% FPL Data: NHANES 2003−08, 200% FPL 1.5 .5 .4 1 .3 Density Density .2 .5 .1 0 0 0 1 2 3 4 5 0 1 2 3 4 5 Score Score Figure : Distribution of Whole Fruit, Whole Grain Components• modewf = 0, modewg = 0Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 26. Results Distributional Concerns• need to address the violation of distributional assumptions• GMM, 2SLS, larger std errs, size of δZ still a concern• finite mixture model (latent class model) – probabilities as function of SNAP participation (in process)Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 27. Results Solution: Bivariate Probit Table : Bivariate Probit: Effect of SNAP on Score >0 Whole Fruit Whole Grain Parameter Marginal Effect Parameter Marginal Effect SNAP 0.672** 0.409 .699*** 0.409 (0.29) (0.22) N 5,105• effect on SNAP is to increase by 40 percentage points points prob of eating any whole fruit or whole grains• too large? less than 30% of sample eat any whole fruit or whole grainGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 28. Results Total Effects: Current RecipientsTable : Total Effects of SNAP (Current) on HEI/Component Scores HEI TotalFruit WholeFruit TotalVeg DkGOrVeg µ -2.371*** -0.301*** -0.570*** -0.059*** -0.019 νµ (0.601) (0.093) (0.137) (0.013) (0.017) TotGrain WholeGrain Milk MeatBeans Oils µ -0.089*** -0.357*** 0.0570*** -0.352*** -0.076*** νµ (0.007) (0.102) (0.004) (0.019) (0.005) SatFat Sodium SoFAAS µ 0.179*** 0.337*** -0.712*** νµ (0.007) (0.028) (0.139) N 5,105Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 29. Results Marginal Effects: Current Recipients Table : Marginal Effect of SNAP (Current) = δZ HEI TotalFruit WholeFruit TotalVeg DkGOrVegδ 5.245 0.897 2.981*** -0.690 -0.674***νdelta (11.316) (1.102) (0.200) (0.514) (0.180) TotGrain WholeGrain Milk MeatBeans Oilsδ 0.053 1.984*** 0.554 -0.264 -0.277νdelta (0.158) (0.073) (0.614) (0.302) (0.934) SatFat Sodium SoFAASδ 0.108 -0.313 0.203νdelta (0.951) (0.542) (2.326)N 5,105• similar marginal effects of SNAP on score > 0.Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 30. Results Robustness: Nutrient Intake Table : Total Effects of SNAP on Nutrient Intake Energy (Kcal) Protein Total Fat Sat Fat Carbsµ -19.78*** -0.047*** -1.810*** -0.221*** 0.711***νµ (1.87) (0.02) (0.31) (0.05) (0.129) Vitamin C Niacin Folate Sodium Frac FAFHµ 8.220*** 0.166*** -0.063*** -0.208*** -0.029***νµ (0.08) (0.02) (0.01) (0.00) (0.00)N 5,105Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 31. Discussion Discussion• Results – SNAP participants slightly lower HEI scores than comparable non-participants – ATE statistically significant, though not economically so – ATE for current recipients somewhat larger–same directions – corroborated by nutrient intake results – however: adverse selection into SNAP – SNAP has positive effect on whole fruit and whole grain consumption of SNAP participants ⇑ in P(Score) > 0. – but participants in general have slightly less healthy diets compared to similar non-participantsGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 32. Discussion Discussion• Further Questions – controlled for endogeneity fully? – distribution of error terms–alternative distributions – how might SNAP improve DQ w/o adversely affecting selection/effectiveness? – subsidies instead of restrictions? (Wholesome Wave, Healthy Incentives)Gregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012
  • 33. Discussion Further Discussion? Thank YouGregory, Ver Ploeg, et al. SNAP and Diet Quality Aug. 13, 2012