Tuesday, April 11, 2006

CDDS Incidence Rate per 10,000



It has come back to me that folks are asking for a incidence rate per 10,000. As you like....

12 Comments:

Blogger Camille said...

That's interesting. There's that big jump in 2000, so that there's like a new baseline, but the size of the fluctuations by quarter are similar, a little more erratic than before 2000. I know that CAN had an ad campaign in 2000 with a child that disappeared from a playground (autism is like having your child kidnapped....). I saw it in early 2001 or late 2000, just as they were starting to get the MIND going (the buildings were a year or two in the future). So Rollens and friends had already started in on the legislature telling them that there had been an epidemic, before that jump... if I remember correctly. That would be interesting to see if the big jump of numbers happened after Rollens started pushing the epidemic to the docs at UCD and to the funding bodies (his old friends in the legislature).

They were hammering on the dangers of thimerosal before 2000 weren't they? Before the numbers went up? Very odd.

It kind of looks like the Wakefiled-causes-autism thing in England.

11:56 PM  
Blogger Joseph said...

There's an artificial population spike in 2002, not sure if that's what Camille is referring to.

In any case, the "incidence" rate per 10,000 is assuming caseload growth is truly "new cases" correct? And this is per 10,000 individuals per quarter.

Prevalence is about 10 per 10,000 it looks like.

2:18 PM  
Blogger Interverbal said...

Camille,

I wouldn't be surprised, that is pretty much what I thought as well.

Now if we could pin down the influecing factor; that would be very cool.

2:24 PM  
Blogger Interverbal said...

Hi Joseph,

Yes, the "new cases" is merely assumed (an very wrongly as the CDDS has told us).

Prevalence is 37 per 10,000 which is a bit higher (but within confidence intervals) of the epi prevalence for Autistic Disorder.

There is an inconsistancy here that maybe we (Camille, you, and I, should think about).

It logically makes sense, that if CDDS autism criteria is more restrictive than DSM-IV Autistic Disorder, than we should see less autism now in the CDDS than in the epi (but we don't). This might be simply be an example of Simpson's Paradox (fancy way of saying "sometimes, we just get different measures").

3:52 PM  
Blogger Joseph said...

Population in California as of 2004 is 35 million. The current caseload is about 31,000. This gives 8.86 per 10,000. Is this correct?

There are a couple things to consider:

1) This is not "classic" autism necessarily.

2) Not everyone persues CDDS eligibility.

The prevalence of mental retardation should be 3% - is that right? Yet, the CDDS caseload only accounts for 0.3%.

Pursuing eligibility for autism vs. mental retardation might not work the same way.

I'm asking CDDS if "autism" only includes "full syndrome" or the other codes as well.

4:10 PM  
Blogger Interverbal said...

Hi Joseph,

Ah, I see, you working off of the whole data set (I was thinking of the 3-5 age group); correct, the prevalence across ages is 8.86 per 10,000.

Your points 1 and 2 are both valid.

You write "The prevalence of mental retardation should be 3% - is that right?"

No, it should be a good deal higher. (I haven't calculated it across the more recent epi, but it looks higher).

"Yet, the CDDS caseload only accounts for 0.3%."

hmmm...That is strange, good catch Joseph.

The CDDS should only (via the Lanterman Act) include DSM-IV Autistic Disorder + further restrictions. That is what they said when I spoke with them.

7:08 PM  
Blogger Joseph said...

You're right. Using the entire population is not a good indicator because of lack of diagnosis in the older groups. If you use the 6-9 group you'll likely find an even higher prevalence. We should use a cohort that matches the cohorts of epidemiological studies.

Regarding MR, I read somewhere that even though 2.5% of so of the population have an IQ below 70, only 0.9% should be considered mentally retarded. And again, we should use younger age groups here.

I strongly suspect CDDS reports do not only list "full syndrome" autism.

7:28 AM  
Blogger jonathan said...

I was wondering if there is any correlation between changes in the schedule of vaccines containing thimerosal and increase in prevalence by birth years in california DDS at all. Looking at the 2003 report it looks like the prevalence more than doubled between birth years of 1970 and 1986 with 4/10,000 for the 1970 group and about 9/10,000 for the 1986 birth cohort yet i don't think they changed the vaccine schedule until about 1988 so apparently there was an incrase before the vaccine schedule changed but people still say there is a correlation so maybe something i don't understand. Any people who believe there is a correlation care to explain this to me?

7:59 PM  
Blogger Interverbal said...

Hi Jonathan,

Yes, there does seem to be correlation, but we don’t know how strong it is as no one has undertaken a statistical analysis of the 3-5 year olds in this group. Some such as Geier & Geier (2006) have looked at all the age groups in their analysis, but this is poor statistical practice.

Remember too, that my graph is looking at 3-5 year olds. So, the oldest birth cohort you will see in my graph were born in 1987.

If one was to graph (I have) all the actual controlled epidemiology (unlike the CDDS which has a lot of errors) the most notable thing will be the uneven up/down trend in the line. The first real spike occurred in 1987. This up/down line behavior may be a function of differing criteria used in the studies.

The real descriptive epidemiologic blow to the vaccine etiology hypothesis, is the fact, that at the moment, we have 3 at least nations (US, UK, Japan) which have the same prevalence of Autistic Disorder, despite their very different vaccine schedules/vaccine types. We might possibly soon add Canada as well (or not).

Point is, the epidemiology is the same internationally and via Chakrabarti & Fombonne (2005) we know the prevalence didn’t change over the course of the 90s which is right in the middle of where many claim that it did.

8:23 AM  
Blogger jonathan said...

you still did not really answer my question. What would account for the changes in prevalance between the birth years of 1970 and 1986 if there was no change in the vaccination schedule during that time? The prevalence rate more than doubled between the two age groups 16 years apart, so even though there was a substantially slower rate of increase than there was when the vaccination schedule was changed in 1988 and then in 1991 there was still an increased prevalence that i don't think can be explained by thimerosal.

As far as the UK is concerned they did not change the vaccine doses but they accelerated the schedule in 1990 giving the vaccines at earlier ages. I don't know as much about the rate of increase in prevalence in birth years in the UK so whether or not there was a lack of correlation is less clear to me as it is for the california data. I am not sure if autism prevalence increased in persons in the UK born before the 90s or not.

8:53 AM  
Blogger Interverbal said...

Hi Jonathan,

“you still did not really answer my question. What would account for the changes in prevalance between the birth years of 1970 and 1986 if there was no change in the vaccination schedule during that time?”

Sorry about that, I misunderstood what you were asking. What could account for the change between 1970 and 1986 is likely to be the advent of DSM-III (1980), in which the concept of autism (and PDDs as well) was broadened.


“The prevalence rate more than doubled between the two age groups 16 years apart, so even though there was a substantially slower rate of increase than there was when the vaccination schedule was changed in 1988 and then in 1991 there was still an increased prevalence that i don't think can be explained by thimerosal.”

That is my conclusion as well.


”I am not sure if autism prevalence increased in persons in the UK born before the 90s or not.”

It is possible, but it seems less and less likely.

11:25 AM  
Anonymous Chrissie said...

Hi there, would it be possible to see the other graph you mentioned that includes all the epidemiology?

9:49 AM  

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