2005_12_11_archive

Autism Epidemic Revisited

I am ambivalent about writing an autism post, since there has been so

much blogbuzz on the topic. Much of the controversy has to do with

two things: the notion that the incidence of autism is increasing, and

the notion that mercury in vaccines has contributed to the increased

incidence of the disorder. The mercury issue has been pretty well

hashed out by Orac, Paul, Skeptico, Autism Diva, and others...too

numerous to count. The "autism epidemic," likewise, had led to an

epidemic of writing -- most of it bad. A Google search on "autism

epidemic" (with the quotes) turns up over 66,000 hits.

And now I've come across another one. It isn't new. It was published

in July 2005 on Medscape. (Medscape articles require registration,

which is free. It is a bit of a nuisance, but Medscape is a pretty

good resource, so it is worth the trouble.) I mention this article

because it may be one of the better articles on the question of

whether the incidence of autism is increasing. Furthermore, it

illustrates some good general points about one of my favorite topics:

skepticism.

Publication Logo Autism "Epidemic?" A Newsmaker Interview With

Morton Ann Gernsbacher, PhD, And Craig J. Newschaffer, PhD

Laurie Barclay, MD

July 15, 2005

-- Editor's Note: Despite heightened media attention on the autism

"epidemic," a report published in the July issue of Current

Directions in Psychological Science offers three arguments against

a true increase in autism prevalence. These include changes in

diagnostic criteria for autism, with current criteria being more

inclusive than when the diagnosis was first defined in the 1940s;

methodological flaws in an unpublished California study widely

cited as showing dramatically increased prevalence; and problems in

using the U.S. Department of Education's annual "child count" data.

To find out more about this issue and its clinical implications,

Medscape's Laurie Barclay interviewed lead author Morton Ann

Gernsbacher, PhD, a Vilas Research Professor, the Sir Frederic

Bartlett Professor at the University of Wisconsin-Madison, and

President-Elect of the American Psychological Society.

For an alternate viewpoint, Dr. Barclay also interviewed Craig J.

Newschaffer, PhD, an associate professor of epidemiology at the

Center for Autism and Developmental Disabilities, Johns Hopkins

Bloomberg School of Public Health in Baltimore, Maryland. Dr.

Newschaffer is lead author of a study using cohort curves to

suggest that autism prevalence has been increasing with time, as

reported in the March issue of Pediatrics. [...]

The article provides a nice balance of viewpoints, all from persons

with decent qualifications. Reading it is a good exercise in critical

thinking. Reading it correctly requires good analytical skills. To

illustrate:

Medscape: What are the significant changes in diagnostic criteria

for autism between 1980 and 1994?

Dr. Gernsbacher: Whereas the 1980 DSM-III entry required satisfying

six mandatory criteria, the more recent 1994 DSM-IV offers 16

optional criteria, only half of which need to be met. Moreover, the

severe phrasing of the 1980 mandatory criteria contrasts with the

more inclusive phrasing of the 1994 optional criteria. For

instance, to qualify for a diagnosis according to the 1980

criteria, an individual needed to exhibit ''a pervasive lack of

responsiveness to other people." In contrast, according to 1994

criteria, an individual must demonstrate only ''a lack of

spontaneous seeking to share.... achievements with other people''

and peer relationships less sophisticated than would be predicted

by the individual's developmental level. The 1980 mandatory

criteria of ''gross deficits in language development'' and ''if

speech is present, peculiar speech patterns such as immediate and

delayed echolalia, metaphorical language, pronominal reversal''

were replaced by the 1994 options of difficulty ''sustain[ing] a

conversation'' or ''lack of varied ...social imitative play."

''Bizarre responses to various aspects of the environment'' became

''persistent preoccupation with parts of objects."

Furthermore, whereas the earlier 1980 (DSM-III) entry comprised

only two diagnostic categories (infantile autism and childhood

onset pervasive developmental disorder), the more recent 1994

(DSM-IV) entry comprises five. [...]

You will see a lot of people debating this point, without really

knowing the details. Some people will say that the increase in

reported rates of autism "couldn't" be explained by changes in

diagnostic methodology or criteria. But it is clear -- once you

understand all the verbiage, that is -- that the changes in diagnostic

criteria were substantial. Not only that, but the diagnostic

categories were broadened, such that milder cases now qualify for a

diagnosis. These are really important points. The point I am making

here is this: you have to know the details, if you are going to make

an informed comment on the subject. This is not one of those areas

where an intuitive guess about the numbers will have any validity; you

can't say the numbers are just too big to be explained by one factor,

and expect anyone to find that persuasive.

Another point is illustrated by the article, one that has nothing to

do with autism. Specifically, skepticism is not merely oppositional

thinking; a good skeptic is comfortable saying "I don't know," when

the evidence is not sufficient to draw a firm conclusion. Similarly,

a good skeptic is comfortable making a tentative decision. Of course,

when one makes a tentative decision, is is necessary to remember that

the decision is not based on solid evidence. Then, one can avoid the

error of establishing complex, important decision trees that do not

have solid roots.

Medscape: Why should we be cautious about this label ["epidemic"],

given changes in diagnostic criteria and in heightened awareness

and recognition of this condition?

Dr. Newschaffer: [...] I believe that there currently is little

strong evidence supporting either hypothesis (real risk versus

diagnostic bias) and that proponents of one versus another

hypothesis seem to hold their view based mainly on the basis of

beliefs that are fallacious - either that the increase has been so

large [that] some of it has to be real, or that the heritable

component of autism is so large [that] the increase over time must

be due to diagnostic changes.

Notice the phrase: "little strong evidence supporting either

hypothesis." In other words, she just plain does not know, and will

not say, which hypothesis is correct. If the evidence is not there,

it is not there. Deal with it. Just don't try to browbeat others

into believing something that is not supported by sufficient evidence,