How To...  Interpret Data  When
Example of Standardization of Race/Ethnicity for a Population Over Time
Background
The prevalence of obesity for children birth to 5 years of age
increased in the state WIC program from 9.4% in 1992 to 11.8% in 2001.
During this time period the race/ethnic distribution in the state WIC
program changed markedly. From 1992 to 2001 the proportion of
white children decreased from 43.1% to 35.2%, and the proportion of black
children decreased from 38.3% to 34.1%, while the proportion of Hispanic
children increased from 17.7% to 29.4%.
In this example, the state WIC program wants to determine if the increase
in the prevalence of overweight from 1992 to 2001 is because of the change
in the distribution of the population especially the increase in the
proportion of Hispanic children who also have the highest prevalence of
obesity. The race/ethnic distribution of the most current or last year
of trend data will be used as the standard because it is most relevant.
Standardization is a technique used to make the population more comparable
on a specific demographic characteristic thus, making the prevalence of
the health indicator of interest also comparable. It will allow you to
determine what the prevalence of obesity for children in 1992 would
have been based on the race/ethnic distribution of the population in 2001.
Therefore, the state prevalence of obesity in 1992 will be standardized
or adjusted based on the race/ethnic distribution of the state in 2001
using the following formula.
Standardization Formula
Σ (A × B) = Standardized
Rate or Adjusted Prevalence
Σ is the sum of A
(proportion of the characteristic in the standard population) multiplied
by B (population characteristic specific prevalence of health
indicator) and equals the standardized rate or adjusted prevalence.
Calculation
The following table will be used to calculate the state standardized or
adjusted 1992 prevalence based on the race/ethnic distribution of the
state in 2001.
Race/Ethnic
Group

Race/Ethnic Distribution in 2001 (Standard)
A
Source: Table 10C

Race/Ethnic Specific Obesity
Prevalence 1992
(%)
B
Source: Table 18C

A × B

White 



Black 



Hispanic 



Native
American 



Asian/Pacific
Islander 



Other 



Adjusted 1992 Prevalence Sum 


Step 1
From the 2001 PedNSS Table 10C, Summary of Trends in Racial and
Ethnic Distribution, obtain the state WIC program distribution of
race/ethnicity in 2001 and list the percent as decimal values defined as "A"
in the table.
Sample: PedNSS Table 10C, Summary of Trends in Growth and Anemia
Indicators
Race/Ethnic
Group

Race/Ethnic
Distribution in 2001
(Standard)
A
Source: Table 10C

White 
.352 
Black 
.341 
Hispanic 
.294 
Native
American 
.001 
Asian/Pacific
Islander 
.010 
Other 
0 

Step 2
From the 2001 PedNSS Table 18C, Summary of Trends in Growth
and Anemia Indicators by Race/Ethnicity, for the state obtain the
race/ethnic specific prevalence of obesity for 1992 and list the
prevalence defined as "B" in the table.
Sample: PedNSS Table 18C, Summary of Trends in Racial and Ethnic
Distribution
Race/Ethnic
Group

Race/Ethnic
Distribution in 2001 (Standard)
A
Source: Table 10C

Race/Ethnic Specific Obesity
Prevalence 1992
(%)
B
Source: Table 18C

White 
.352 
7.9 
Black 
.341 
9.5 
Hispanic 
.294 
12.6 
Native
American 
.001 
10.6 
Asian/Pacific
Islander 
.010 
7.8 
Other 
0 
0 
Adjusted 1992 Prevalence Sum 

Step 3
Multiply the proportion for each race/ethnic group for the
state in 2001 (A) by the state obesity prevalence in 1992 for
each corresponding race/ethnic group (B); the sum of the product
of A × B for each race/ethnic group is the adjusted prevalence
for overweight for the state in 1992. The table below shows this
calculation for each race/ethnic group.
Race/Ethnic
Group

Race/Ethnic Distribution in 2001 (Standard)
A
Source: Table 10C

Race/Ethnic Specific Obesity
Prevalence 1992
(%)
B
Source: Table 18C

A × B

White 
.352 
7.9 
2.78 
Black 
.341 
9.5 
3.24 
Hispanic 
.294 
12.6 
3.70 
Native
American 
.001 
10.6 
.01 
Asian/Pacific
Islander 
.010 
7.8 
.08 
Other 
0 
0 
0 
Adjusted 1992 Prevalence Sum 
9.82 

Summary
The adjusted prevalence for obesity for the state WIC program in
1992 is what the prevalence would have been based on the race/ethnic
distribution of the state in 2001. The adjusted prevalence of obesity in 1992 is 9.8%, slightly higher than the original prevalence of 9.4%
indicating that the change in the distribution of the population from
1992 to 2001 contributed marginally (0.4%) to the increase in overweight
during this time period. Therefore, the change in the distribution of
the population from 1992 to 2001 did not affect the prevalence of
obesity .
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Page last reviewed: October 29, 2009
Page last updated: October 29, 2009
Content Source: Division of Nutrition, Physical Activity and Obesity,
National Center for Chronic Disease
Prevention and Health Promotion
