WASHINGTON — Secretary of Agriculture Tom Vilsack on Oct. 15 said the U.S. Department of Agriculture has selected Princeton, N.J.-based Mathematica Policy Research to conduct a major survey on food choices and expenditures by U.S. households — the National Household Food Purchase and Acquisition Study (NHFPAS). Mathematica Policy Research is a nonpartisan firm that conducts research and surveys in health care, education, welfare, employment, nutrition, and early childhood.

"Helping American families improve their overall health is one of my top priorities," Mr. Vilsack said. "This ambitious 5-year effort will fill in critical gaps in existing data on the food purchases of U.S. households and be invaluable in assessing and enhancing the effectiveness of USDA’s food assistance programs for low-income families."

The U.S.D.A. said its Economic Research Service and Food and Nutrition Service will work together to use the data collected by Mathematica Policy Research to study how food assistance programs and other economic and demographic factors affect household food purchase decisions and health outcomes.

The data that will be used has not been available previously to researchers, the U.S.D.A. noted.

"For the first time, researchers will have data that captures key factors like food prices, where food is purchased, dietary knowledge, and the interplay of food assistance programs and food choices," said Rajiv Shah, undersecretary for Research, Education, and Economics at the U.S.D.A.

The launch of the survey comes on the heels of an E.R.S.-led study on the problem of limited access to nutritious food. The latter study addressed the issue of "food deserts," or areas with little or no access to retail outlets providing healthful food. The new U.S.D.A. food purchase survey is expected to allow the E.R.S. to further analyze how lack of access and retail outlet choice and location influence households’ food purchases and dietary quality.

Other issues expected to be addressed by the survey include:

• How price and income influence food choices and the dietary quality of food purchases;

• What participants in the SNAP, formerly the Food Stamp Program, buy and how much it costs;

• How participation in food assistance programs influences food purchases;

• The relationship between food purchase decisions and levels of food security (consistent access to sufficient food for a healthy lifestyle);

• How access and retail outlet choice and location influence food purchases and the resulting dietary quality of purchases; and

• The influence of nutrition knowledge on food purchases.