What is the cost of a healthy diet?
Linking USDA nutrient and food composition data to retail sales data
The U.S. Department of Agriculture (USDA) uses food purchase data for a number of research and policy initiatives, and also produces databases of the nutrient composition of foods.
In order to associate sales data with nutrient data, USDA needs to link the 2 data sources. These links enable research on healthy food purchases and estimation of the costs of foods reported by participants in What We Eat in America, the dietary intake component of the National Health and Nutrition Examination Survey (NHANES). The challenge is to link 2 data sources that use different terminology to describe foods.
Westat developed food category-specific tables linking text terms used in the 2 databases and an algorithm to identify the most likely one-to-one match between the sales data item and a nutrient data item.
Westat nutritionists reviewed the matches for accuracy and manually assigned matches when an automated match failed. They also developed a database of yield factors to convert the weight of the food as purchased (e.g., raw chicken with bones) to the weight of the food in the nutrient database (e.g., raw chicken without bones).
Westat also developed procedures to estimate national average prices for each food reported in What We Eat in America.
The links between sales and nutrient data and the methods for developing national average prices allowed USDA to update the cost of the U.S. Thrifty Food Plan, the basis for the Supplemental Nutrition Assistance Program (SNAP) benefits. The use of the linked data resulted in increased benefits for SNAP recipients.
USDA plans to use the linked data to further analyze food purchases and will also make the linked data available to other government and private researchers, enabling wide-ranging research on food costs and diet quality.
Development of the Purchase to Plate Crosswalk and Price Tool: Estimating Prices for the National Health and Nutrition Examination Survey (NHANES) Foods and Measuring the Healthfulness of Retail Food Purchases
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