ESTIMATING THE PROPORTION OF VITAMIN A DEFICIENCY AMONG CHILDREN AGED 6 MONTHS TO 5 YEARS

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1 ESTIMATING THE PROPORTION OF VITAMIN A DEFICIENCY AMONG CHILDREN AGED 6 MONTHS TO 5 YEARS Allan A. Gulles Master of Statistics ABSTRACT Background: Vitamin A deficiency (VAD) is the leading cause of preventable blindness among children and increases the risk of disease and death from severe infections according to the World Health Organization. The 2003 National Nutrition Survey (NNS) was designed to provide estimates at the national level and there is a need for sub-national estimates for nutrition and health program planners and implementers. Objective: The general objective of this study is to obtain reliable estimates of the proportion of Vitamin A deficiency among children aged 6 months to 5 year old at the provincial/city level of the Philippines. Specifically, this study aims to: a) generate reliable estimates of the proportion of vitamin A deficiency among children aged 6 months to 5 years using direct estimation technique and indirect estimation technique and b) evaluate the estimates obtained from the different methods in terms of accuracy, precision, and reliability. Methods: In this study, estimates of the proportion of vitamin A deficiency among children aged 6 months to 5 years at the provincial/city level were obtained using direct and indirect estimation techniques, using the 6th National Nutrition Survey (NNS) data. Auxiliary variables used came from the 2000 Census of Population and Housing (CPH) and other administrative data. The indirect estimation techniques, specifically the empirical best linear unbiased prediction (EBLUP) with regression synthetic estimates as the model-based estimates were used. The regression synthetic estimation models evaluated were: Ordinary Least Squares (OLS) Regression, Principal Component Regression (PCR), Poisson Regression, and Mixed Model with province as random effect. Estimate of VAD with CVs not higher than 10% was considered reliable. Result: The direct estimates were found to be unreliable since estimates in only % of the provinces had a coefficient of variation of at most 10%. For the EBLUP estimates, OLS had % provinces with reliable estimates of VAD; Mixed model had 100% of the provinces with reliable estimates; and PCR had % of the provinces with reliable estimates. Poisson estimates resulted to 4.65% of the provinces with reliable estimates of VAD. Conclusion: In general, the indirect estimation technique produced more reliable estimates than the direct estimation technique. Recommendation: Results of the study indicated that indirect estimation techniques, particularly the EBLUP Mixed model, provided the best alternative means of estimating provincial incidence of vitamin A deficiency among children aged 6 months to 5 years per thousand.

2 INTRODUCTION Vitamin A deficiency (VAD) is the leading cause of preventable blindness in children and increases the risk of disease and death from severe infections according to the World Heath Organization. Vitamin A deficiency is a public health concern in more than half of all countries, especially in Africa and South- East Asia, hitting hardest young children and pregnant women in low-income countries. In the Philippines, among children aged 6 months to 5 years, vitamin A deficiency is prevalent in 13 out of 16 regions in the country according to the 1998 National Nutrition Survey conducted by the Food and Nutrition Research Institute of the Department of Science and Technology (FNRI-DOST). Since most of the decision-making process is done at the sub-national level, there is a need to provide reliable statistics at this level. The lack of financial resources constrained the sample selection that could have allowed estimation for all provinces. Small area estimation procedures provide some alternative options in the generation of estimates at the provincial level. These techniques make uses of administrative and/or census data, in combination with survey data to produce more reliable estimates for smaller areas. OBJECTIVES General: To obtain reliable estimates of the proportion of Vitamin A deficiency among children aged 6 months to 5 year old at the provincial level Specific: To generate estimates of the proportion of vitamin A deficiency among children aged 6 months to 5 years using direct estimation method and small area estimation technique To evaluate the estimates obtained from the different methods in terms of measures of accuracy, precision and reliability METHODS Data Source VAD - 6th National Nutrition Survey (6th NNS) from the Food and Nutrition Research Institute (FNRI-DOST) Auxiliary variables Census of Population and Housing from the National Statistics Office (NSO)

3 Direct Estimation The direct estimator in the ith province is define as the ratio of the estimated total number of vitamin A deficient children aged 6 months to 5 years to the estimated total number of children aged 6 months to 5 years, is given by: NPi Pi= Ni Ordinary Least Squares Regression The OLS regression model takes the form: Ŷ=β0+β1x1+ β2 x2+ +βpxp Where Ŷ=E(Y/X) I is the mean response and (j=0, 1, 2,, p) are unknown parameters. Poisson Modeling The Poisson regression model takes the form: Log(μ)= β0+β1x1+ β2 x2+ +βpxp where μ is the mean response and (j=0, 1, 2,, p) are unknown parameters. Mixed Model The mixed model takes the form: Ŷi= βijxij+τi J=0 Where τi is random provincial effect component. The auxiliary variables were assumed to have fixed effects. Principal Component Regression Model The Principal Component Regression model takes the form: Ŷi= β0 βki T ki K=1 where T is the kth principal component score for the ith observation, a is the number of principal components. Empirical Best Linear Unbiased Prediction The EBLUP estimator of the proportion of vitamin A deficient children aged 6 months to 5-year of the ith province is of the form: + (1+Yi) p I

4 RESULTS Top 5 provinces with the highest prevalence of VAD Top 5 provinces with the lowest prevalence prevalence of VAD Province Incidence per thousand CV (%) Province Incidence per thousand CV (%) Mt. Province Marikina Zamboanga sibugay Tawi-Tawi Nueva Ecija Davao Oriental Abra Ilocos Norte Palawan Cebu Distribution of the incidence of of VAD by province Distribution of the incidence of VAD by province by EBLUP technique Incidence of VAD Distribution(%) Frequency Incidence of VAD OLS Mixed PCR Less than to < to < to < to < to < and over Less than to < to < to < to < to < and over Distribution of coefficients of variation of the provincial estimates of VAD Distribution of coefficients of variation of the provincial estimates of VAD by EBLUP technique Coefficient of Variation Distribution(%) Frequency Coefficient of Variation (%) OLS Mixed PCR At most to to to to and over At most to to to to and over

5 CONCLUSION and RECOMMENDATION The direct estimates were not considered reliable because of high CVs. The CVs of the estimates were also found to have a skewed distribution. Furthermore, provinces with supposedly reliable estimates were mostly due to very high estimates of incidence of VAD and not due to small standard errors. Results of the study indicates that indirect estimation techniques, particularly the regression synthetic and EBLUP method, provide alternative means of estimating provincial incidence of vitamin A deficiency among children aged 6 months to 5 years per thousand. Simulation procedure can be done to estimate the reliability (e.g., MSE, CV) of the EBLUP for Poisson. The VAD estimates from the EBLUP mixed are very similar to that of the direct estimates. The coefficients of variation are very small showing that it is very reliable. It is recommended to use EBLUP mixed estimates as an alternative because of its reliability.