Task 1b: How to Generate Age-Adjusted Prevalence Rates and Means Using SAS 9.1 Survey Procedures

In this task, you will generate age-adjusted prevalence rates and standard errors for high blood pressure (HBP) by sex and race in persons 20 years and older. An optional second example is available demonstrating how to generate age-adjusted means and standard errors for Body Mass Index (BMI) by sex and race/ethnicity for persons 20 years and older.

To calculate age-adjusted prevalence rates, you will need to know the age standardizing proportions that you want to use, and then apply them to the populations under comparison. This is called the direct method for age standardization. Typically, Census data are used as the standard population structure.  For age standardization in NHANES, NCHS recommends using the 2000 Census population.  A spreadsheet with the year 2000 U.S. population structure by age is attached below.  The standard age proportions are calculated by dividing the age-specific Census population (P) by the total Census population number (T). The standardizing proportions (P/T) should sum to 1 (please see the table below for the standard age proportions used in this module.)

Attachment

For your convenience, standard proportions for different NHANES population age groupings are provided in the Excel spreadsheet attached below. This file uses the 2000 Census as the standard population.  The adjustment factors were calculated for four age groupings:

1. all ages,
2. ages 6 years and older,
3. ages 20 years and older using 10 year age intervals, and
4. for the blood pressure example in this module, for ages 20 years and older using 20 year age intervals.

For other age groupings, you can combine the smaller age groups provided in order to reflect the age and subpopulation you are using in your analysis.

Standard Proportions for NHANES Population Groupings link: ageadjtwt.xls

Example of How to Calculate Standard Age Proportions

Here is an example of how to calculate the standard age proportions by dividing the age-specific Census population (P) by the total Census population number (T). The standardizing proportions should sum to 1.

Standard Proportions for 20-year Age Groups Based on the 2000 U.S. Census Standard Population

As you can see each "standard age proportion", also referred to as “age adjustment weight”, is simply the proportion of people in the 2000 Census - the standard population - in a specific age category.  For example, the standard age proportion for people 20-39 years old is:

Equation for the standard age proportion for people 20-39 years old

Reference

Klein RJ, Schoenborn, CA. Age Adjustment using the 2000 projected U.S. population. Healthy People Statistical Notes, no. 20. Hyattsville, Maryland: National Center for Health Statistics. January 2001.

Step 1: Download SAS %sregsub Macro Text File