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ERS Food Availability Data Under
Revision
Jean
Buzby, Janet
Perry
The ERS per capita
food availability data are a historical
series that measure the national food
supply of several hundred foods. It
is the only source of time series data
on food availability in the country.
The per capita food
availability data are most commonly
used to:
• Estimate the
average level of food consumption in
the country,
• Show year-to-year changes in
the estimated consumption of major foods,
• Establish long-term consumption
trends, and
• Assess changes in food consumption
relative to major nutrition or policy
initiatives.
The food availability
data measure food use of basic commodities,
such as wheat, beef, and eggs, as measured
at the farm level or at an early stage
of processing. They do not measure food
use of highly processed foods, such
as bakery products, frozen dinners,
and soups, in their finished product
form. Their ingredients, however, are
included as components of less processed
foods, such as sugar, flour, vegetables
for processing, and fresh meat.
Constructing
the Data
The food availability
series is based on records of annual
commodity flows, from production to
end uses. This involves developing supply
and use “balance sheets”
for each major commodity from which
human foods are produced. In general,
the total annual available supply
of each commodity consists of the sum
of production, imports, and beginning
stocks. The amount of food available
for human consumption is usually calculated
as the difference between available
commodity supplies and nonfood use.
For most commodity categories, measurable
nonfood uses are farm inputs (feed
and seed), exports, ending stocks, and
industrial uses. The components of the
balance sheets are either directly measured
or estimated by government agencies
using survey sampling and statistical
methods.
As an example of these
calculations, ERS has published potato
supply and use data starting in 1960
for fresh and processing potatoes (i.e.,
freezing, canning, chipping, and dehydrating
potatoes). (Sweet potatoes are estimated
separately.) ERS bases its estimates
of the availability of potatoes for
consumption entirely on production and
net trade because data on beginning
and ending stocks are not available,
except for frozen potatoes. USDA’s
National Agricultural Statistics Service
provides survey data on production and
frozen stocks, and the Census Bureau
provides the trade data. Per capita
use of potatoes is calculated as total
domestic availability divided by total
U.S. population (including armed forces
overseas) on July 1, as reported by
the Census Bureau.
The food availability
data are a commonly used proxy for food
intake because there are no comprehensive
time series data on human food use for
the hundreds of commodities covered
by this database. The food availability
data are not affected by the problems
implicit in consumer survey data, such
as bias from inaccurate self-reporting
of food intake by consumers. In short,
the food availability data provide an
independent basis for examining changes
in food consumption patterns if waste
and other losses in the system are relatively
constant over time. Additionally, trends
in per capita food availability can
be used to test the hypotheses that
government and general sources of diet
and health information influence consumers'
food choices.
Conversion
Factors Under Revision
One source of error
in the food availability data lies with
the retail conversion factors used to
estimate per capita consumption. The
conversion factors used in this data
series are rough approximations of weight
loss of a commodity from the farm to
the retail level. For example, the conversion
factor used to convert the weight of
fresh potatoes at the farm level to
the eventual weight of fresh potatoes
sold at retail is estimated at 96 percent.
Whereas the retail conversion factor
for canned potatoes is around 64 percent.
Much of this difference is due to the
peeling, cutting, and trimming required
to produce various canned potato products.
In general, precise
information to estimate and update conversion
factors is lacking. The way foods are
produced, marketed, and sold has changed
over time. For example, some vegetables,
like fresh asparagus, are now harvested
and bagged on the farm, which means
less waste in processing and a higher
conversion factor from farm to retail.
ERS, in collaboration with The Food
Industry Center at the University of
Minnesota, has undertaken a high-priority
effort to systematically update conversion
factors at the retail level. Using input
from various members of the food industry—processors,
packers, wholesalers, and retailers—will
yield more accurate conversion factors
and thus a more thorough understanding
of how commodities are transformed into
consumer products.
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Behind
The Data
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