Understanding the population sample represented in CDC WONDER database

Question

I’m trying to understand the population numbers in the CDC WONDER database when querying information regarding STD morbidity.

If I build the following query:

• Age: 20-24 years
• Disease: All
• Gender: All
• Race/Ethnicity: All
• State: Illinois (17)
• Year: 2011
• Group By: Disease
• Show Totals: True
• Show Zero Values: False
• Show Suppressed: False
• Calculate Rates Per: 100,000

The results return the following:

It's not clear to me what the quoted population sample is. The website documentation cites sources but not how they are used.

Additionally, in the image supplied, I don't understand why the last line was totaled for the population. Shouldn't the total "Rate per 100,000" be 3,422.21 instead of 1,140.74?

(30,080 / 878,964 * 100,000) = 3,422.21

Answer 1

I would go with the population denominator of 878,964. According to the Census Bureau, the 20 to 24 year old 2011 population in Illinois was 881,738.

As to your second issue, just remember that it only makes sense to combine them when you are looking for rate of cases among the population. If you want to reference it as the rate of chlamydia among the population, you would have to keep it separate from the calculation of gonorrhea because some people might have both. The best practice would be to only reference them as separate rates. Ignore whatever CDC wonder is doing with the sum total at the bottom. It is probably a programming oversight.

Let us know if you're looking for any more information.

Answer 2

The total population for Illinois in 2010 Census is 12.8 million. The 2.6 million should be for adults 20 to 24 years old.

http://quickfacts.census.gov/qfd/states/17000.html

The rate per 100K for these age group would be the total cases for the age group (30,080) divided by the population for the age group (2,636,892) which is 1.14% rate or 1,140 per 100K.