Friday, October 07, 2005

Reviewing the Autism Prevalence (The Epidemiology: Part 2)

If upon reviewing the evidence, we take the stance that there is no epidemic of autism, we can be asked the totally reasonable question of why there appears to be an increase. I have already made some answers concerning the use of the IDEA and California DDS data; in this post I will discuss the change in the epidemiology statistics.

The first thing to note is the difference between studies over the years. In fact wide discrepancy can be observed in the Autistic Disorder specific prevalence per 10,000 persons in the whole world. This includes (.7) calculated by Treffort (1970) using criteria established by Dr. Kanner’s (The person who first described Autism) observations. Sugiyama & Abe (1989) calculated (13) using The Diagnostic and Statistic Manuel-III (DSM) criteria. This can be compared to the greater prevalence of (72.6) calculated by Kadesjo, Gillberg, & Hapberg (1999) using The DSM-III and the Revised International Disease Classification-10 (ICD).

The ICD-10 and the DSM-IV have some discrepancies and although close, are not totally comparable. When viewing studies that offer a rate of all the Pervasive Developmental Disorders, a range can be found from (11.2) per 10,000 persons (Fombonne, & du Mazabrun, 1992), through (67.4) (Bertrand et al., 2001). The problem with these data is that they are calculated from different diagnostics, some of which are more stringent and that they used population samples of different sizes.

Fombonne (2003) lists the prevalence rates of 32 Autism Epidemiology studies from (1966-2001). These are listed in tables (I, III) within (Fombonne, 2003). These data are taken on world wide epidemiology. I calculated the means of these studies by decade, because an increase can be observed this way. It should be noted that the specific decade mean, that a study was placed in this paper, was determined by the year it was published and not the year of the actual data collection.

Fombonne (2003) lists the prevalence rates of 32 Autism Epidemiology studies from (1966-2001). Based on this I calculated the mean in the 1970’s at (3.27) per 10,000 (Standard Deviation =2.24). I calculated this in the 1980’s at (6.98) per 10,000 (SD=5.12). I calculated this in the 1990’s at (19.26) per 10,000 (SD=22.5). I calculated this in the year’s post 1999 at (21.06) per 10,000 (SD=11.78).

The standard deviations are very large in comparison to the means. In the 1990s the standard deviation exceeded the mean. This is an indication of the very discrepant results within this decade. In years post 1999 the standard deviation decreases, showing a greater consistency of the studies.

Using table (3) in the Fombonne (2003) display of studies that calculate Pervasive Developmental Disorder, I calculate the mean in the 1970’s at (13.7) per 10,000 (SD=10.61). I calculated this in the 1980’s at (8.5) per 10,000 (SD=2.96). I calculated this in the 1990’s at (13.75) per 10,000 (SD=3.61). I calculated this in the year’s post 1999 at (49.8) per 10,000 (SD=20.2). In this case the 1970s research seems to have more variation than the more recent decades.

This analysis does not include the most recent epidemiology, specifically Chakrabarti & Fombonne, (2005). However, this study should not significantly affect the standard deviation and mean. It will raise the mean slightly towards the prevalence predicted in Chakrabarti & Fombonne, (2005).

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4 Comments:

Blogger Ed in Colorado said...

If there is an epidemic, then there must be a cause that is not genetic. The cause has to cover the time and the geography of the epidemic. Aside from vaccines, the medical community has nothing that fits that criteria. If it can't be vaccines, the CYA manual says that there can't be an epidemic.
So where are the older autistics? The states should be overwhelmed by autistics who have reached the age when their parents can no longer take care of them. Where are they?
I keep hearing about these wonderful peer reviewed studies that show that there is no relationship between autism and mercury or autism and vaccines. Show me the one with a control group, the group that did not have vaccines. What was the autism rate in that group compared to the group that was vaccinated with thimerosal laden shots. Where is it? What was the rate in the control group?
When I am shown manipulated statistics, I feel that someone is trying to manipulate me.

11:01 AM  
Blogger Interverbal said...

Hi Ed,

This post was about how we know that an epidemic of autism exists or doesn't. It was not an argument about a cause of autism (I did write such an argument yesterday on this blog though).

My interest is epidemiology, not thimerosal, that said, I think thimerosal advocates have attached themselves so closely to an "epidemic", that I am not sure that their theory can stand in the absense of an epidemic.

You wondered where the all the older autistics were. Possibly recieving services (or not) under a different category. Also, please check out tbis post http://interverbal.blogspot.com/2005/10/reviewing-autism-prevalence-use-of.html
and click on the graph with the heavy red line. Now follow that red line as it follows the 6 year old cohort in 1996 as they become the 13 year old cohort in 2003.

All the studies I cited are peer reviewed, but all they do is show the prevalence rate based on the the definitions the authors used, not a valid/invalid mercury connection, which is a seperate issue.

I can not quite tell, but I infer that you are referring to my statistics when you speak of "manipulated statistics". I had this hope that, because I was religiously citing and refering all my sources, that anyone who disagreed would check those first, before speaking of manipulation.

There is nothing to stop you from checking out my sources and running calculating the same stats to double check my work, you should probably do that.

3:04 PM  
Blogger Ed in Colorado said...

What I refer to are the "peer reviewed studies" that I have seen coming out of the medical community. The first example was the Danish study, which was cited by the IOM. If you believed the statistics, then thimerosal helps prevent autism. It reached the right conclusion and was not questioned by the peers. When I see studies that are clearly flawed and still pass peer review, I have to question the legitimacy of the peer review.

So again, I ask for something simple - a control group. You have obviously looked at more epidemilogical studies than I have. Does such an item exist? What was the autism rate in the control group, the one that never got vaccines? I would expect to see it on the front page if the control group showed the same autism rate as the general population. I haven't seen a control group, but I have seen references to studies where the people who had not received vaccines were thrown out of the study. That just adds to my doubts.

I don't question your homework. But the medical community produces these statistics and they have their oar deep in the water. And yes, they have manipulated the statistics to show that there is no connection. The peer reviewed studies had the statistics I was referring to.

I am frustrated and I gave you the blunt end of it. For that I apologize. But there are so many things that require research by the medical community - leaky gut, leaky blood brain barrier, low levels of glutathione, metallothionine, processing of heavy metals by autistic children, just to name a few. Each of these is measurable. But it might point to an autism mercury connection. The medical community will not touch it. That leaves the autism community hanging from a cliff while they sit there.

As for the epidemic, let's turn that around. If there is an epidemic, genetics might contribute, but there has to be something more. And that something more has to fit into the geography and the timing of the epidemic. It can't be vaccines therefore it can't be an epidemic.

4:24 PM  
Blogger Interverbal said...

Hi Ed,

The Danish studies are correlational, they do not establish or fail to establish mercury causality. I am aware there a conflict of interest in the Danish studies. If I remember correctly this has been indicated, as is proper procedure. Also, conflict of interest is not, in and of itself enough to invalidate a study.

In any kind of post event study, we can include a control group, but the design would still be correlational in nature. This provides limited evidence either way.

I have looked at mostly epidemiology of prevalence or incidence, as opposed to correlational studies looking at thimerosal and autism (which are sometimes called epidemiology).

Can you tell me more about the studies where folks without vaccines were tossed out.

Remember, it is not only the medical community, but also the psychological community who produces the epidemiology. There is no reason to think they have been manipulated, in fact most persons think upon first looking at them, that they show an epidemic.

Blunt speech never offends me by the way. I do demand precision from other scientists though, I think this is a “responsibility” issue for those folks and for me.

I agree that all those things you mention can be studied, but on whom does the burden of proof fall?

I have noted your statement “It can't be vaccines therefore it can't be an epidemic”, several times now, both here and on your own site. However, in my case, it is just the opposite. I got into epidemiology first, and it remains one of my primary interests.

I don’t know if thimerosal causes autism, but I have problems with an un-researched treatment to remove mercury and I take the stance that the facts indicate there is no epidemic of autism.

6:39 PM  

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