Demographics:
How Can This Information Help Me?

Consumer Expenditure data measure the likely expenditure for a product
or service in a county, ZIP Code, or other trade area. The files include the
average expenditure per consumer household, total expenditures, and a
Spending Potential Index (SPI). The index compares the average
expenditure for a product or service locally to the average amount spent
for the product or service nationally. The index is tabulated to represent a
value of 100 as the average. An index higher than 100 shows higher
spending; an index less than 100, lower spending (relative to the U.S.
average). For example, an index of 120 shows that average spending by
consumers in the trade area is 20 percent higher than the U.S. average; an
index of 85, 15 percent lower than the U.S. average. 

You can use the information to answer questions such as these:

How much money do the people in the study area spend on my kind
of product? 
How does that compare to the average? 
Do they seem to have discretionary income?        
How Is the Information Gathered?

The following equation shows how the index is derived. For trade area "t",

SPI = Local Average Expenditure X 100 / U.S. Average Expenditure 

CACI’s consumer spending data are calculated from the Bureau of Labor
Statistics’ Consumer Expenditure Interview Survey (CEX). CACI
extracted demographic and economic data for households from the CEX
Interview Surveys, 1993-1994, to construct a conditional probability
model. The model links the spending of consumer units or households
surveyed in the CEX to all households with similar socioeconomic
characteristics. Spending patterns are further differentiated by geography --
region of the U.S., urban v. rural, and metropolitan v. nonmetropolitan --
and updated to current prices using the annual Consumer Price Index.
Expenditures represent annual averages or total expenditures.