I needed confirmation of my numbers for a post I am writing. It is serious enough that I wanted to be sure before going ahead.

Here is what it looks like

http://lh6.ggpht.com/_WoSi1HFM.....0/NSCH.gif

There is one article in, I believe, “Multiculturalism” which addresses racial/ethnic differences in the IDEA data. The MMWR’s from the CDC show dramatic racial/ethnic divisions in autism prevalence. The IDEA raw data show very large differences in prevalence depending on ethnicity.

It is quite clear that IDEA data are not an accurate count of the actual number of autistic children. Never has been. One can derive some trends, but one must keep in mind the limitations.

I am sorry that I may have contributed to some of the confusion here by not including an autism prevalence graph on the autism rates page and not providing enough documentation on the terms, calculations, and graphs on the FightingAutism website.

How is the crude incidence calculated in the graph?

Crude incidence is calculated by subtracting two consecutive school years autism administrative prevalence to get the change in autism administrative prevalence for each age. For example, the crude incidence for 16 year olds is calculated by subtracting the autism administrative prevalence of 16 year olds in 2006-2007 from the autism administrative prevalence of 16 year olds in 2007-2008. So it is literally the change in the autism administrative prevalence between consecutive birth cohorts. The crude incidence calculation assumes nothing – it is just a calculation. Perhaps, “prevalence change” would be better terminology.

Since the autism administrative prevalence is already normalized for population size (i.e per 10K births) the crude incidence is normalized for population change between the consecutive birth cohorts.

I’d love to hear how you explain the geographic differences

I would defer to http://www.springerlink.com/co.....6788316g8/

I’d love to hear how you explain the race/ethnic differences

I have not looked at race/ethnic differences yet. Can you provide me with some references?

Thanks, Dan
Dan Hollenbeck

It doesn’t really give you any insight into why something is changing, just whether it is changing and how the rate of change is varying as a function of time.

It allows you to measure population growth; that’s it. It should not be called incidence, crude or not. That’s something else. Additionally, if you want to measure population growth, the answer needs to be expressed as a percentage, e.g. 20%. Saying it’s 20 in 10,000 is meaningless. You need to know the size of the population to determine the meaning of that number. If the population grew by 20 in 10,000, but it was already 200 in 10,000, that’s obviously not the same as if the population was 10 in 10,000.

BTW, how is the crude incidence calculated in the graph? If it’s divided by the whole population, 20 in 10,000 is ridiculously high. Whole population incidence of autism in the US should be around 1 in 10,000 per year, if awareness is stable.

How is crude incidence for 16 year olds calculated? Is it by calculating the number of teens who got diagnosed when they were 16?

Your current comparison against the TH data is even worse – the data not only isn’t the same exact question it doesn’t even represent the same thing or the same time period.

Yep. You are right. I am comparing some fairly straightforward data to some mashup that, as Joseph points out, makes no sense.

Compare the NCHS data to any data you like which “shows” an epidemic. Explain why the autism counts are pretty much flat in the NCSH data.

Go ahead and do the 2003 vs. 2007 comparison. Explain to me why the 1990 birth year group had a 0.48% “prevalence” in 2003 and 0.88% in 2007. You see, I already have that dataset open.

edited to add:

The 2003 survey asked the question Has a doctor or other health professional ever told you that [selected child] has autism”

The closest comparison to the 2007 survey would be the quesiton, “”Has a doctor or other health professional ever told you that [selected child] has autism, Asperger’s disorder, pervasive developmental disorder, or other autism spectrum disorder?”

These would give “rates” for kids born in 1990 of: 0.46% (for the 2003 dataset) and 1.45% (for the 2007 dataset)

In my original example in this response, I mistakenly used the 2007 question: “does [selected child] currently have autism or ASD]. That has a rate of 0.88%

So, if anyone would like to explain why the number tripled from 0.46% to 1.45%, I’m open to ideas. The broadening of criteria seems an obvious first step. The possibility that more kids were diagnosed—even after age 13—is open as well.

Your current comparison against the TH data is even worse – the data not only isn’t the same exact question it doesn’t even represent the same thing or the same time period.

Besides, I would be surprised if the data from 2003 did not already reflect PDD-NOS and Asperger in addition to classic autism. My children all are PDD-NOS but if someone asked me if they had autism I would say yes. I think most parents would do the same.

I think I will do the comparison regardless even if you won’t. it will be interesting to see if the increases are across the board or concentrated in certain age groups.