Sunday, March 19, 2006

No Autism Epidemic: Summary of the Numerical Evidence

[Note: For an updated analysis, see No Autism Epidemic: An Update]

In prior posts I have argued in favor of the idea that an autism epidemic has not occurred at all. In this post I will put everything in one place, include additional data, and clarify a few points. As always, readers are invited to scrutinize the data, my interpretations of the same, and post comments and/or rebuttals. In particular, all epidemic-causing-trigger proponents are explicitly invited to do so.

Proponents of the idea of an autism epidemic often rely on data from the California Department of Developmental Services (CDDS). But as you will see, this same data contains a wealth of information that can be used to disprove that such an epidemic ever took place.

Changing Characteristics

There is a problem of group inequivalence in equating number of diagnosed cases with actual prevalence and number of new diagnosed cases with actual incidence. What this means is that the characteristics of diagnosed autistics over time have changed, so comparing the number of diagnosed individuals from one quarter to the next is like comparing apples and oranges (or oranges to sheep).


Table 1: Changes in autistic client characteristics over time
QuarterEpilepsyProfound MRSevere BehaviorsLack of MR
Q2 199215.6%11.2%22.9%27.8%
Q4 199611.8%7.4%20.5%41.2%
Q4 20008.7%4.4%19.2%52.4%
Q4 20047.1%2.6%17.4%61.9%
Q4 20056.7%2.4%16.8%63.6%


Table 1 not only shows that it is not possible to make an accurate determination about prevalence and incidence changes, it also shows that a significant 'broadening criteria/awareness' phenomenon must be in effect. This is undeniable given this data. The following figure [courtesy of CDDS] also illustrates the point. Notice that the autism curve and the autism without MR curve run almost parallel to one another.






Broadening criteria does not imply that autistics diagnosed today who would not have been diagnosed in prior years are completely neurotypical. It simply means that the proportion of certain characteristics must be closer to those of the general population. Judging from the size of the autistic population and drops in these numbers it would appear that newly diagnosed autistics today are, in average, considerably less autistic than those at the beginning of the 'epidemic'. This completely undermines any epidemic-causing trigger theory.

Regional evidence

[Note: For an updated regional analysis, see Regional Differences and Quarterly Growth Due to Two Factors.]

In a previous post on regional differences I argued that they cannot be explained by environmental factors because of group inequivalence. In particular, the Central Valley (Fresno) Regional Center has the lowest prevalence of diagnosed cases of autism, whereas the Westside (West LA) Regional Center has the highest prevalence. Even so, there is no difference in the prevalence of mental retardation in these Regional Centers (using epilepsy as a baseline, as it is assumed to be uniformly diagnosed). This is illustrated in Table 2.

Table 2: Q4 2005 comparison of Westside and Central Valley
Regional CenterAutism IndexPMR+SMR IndexPMR IndexEpilepsy IndexSevere Behavior Index
Central Valley0.320.600.361.00.31
Westside1.610.680.311.00.45


[Note: A diagnosis of 'severe behaviors' likely suffers from subjectivity as well, and is probably not, by itself, sufficient to fulfill CDDS eligibility criteria. In any case, a purely behavioral mini-epidemic could be ruled out by separating a Central Valley-equivalent group in Westside and evaluating differences in behavior.]

Group inequivalence is clear, but it is also clear that there is probably no difference in actual prevalence or incidence of autism between these two Regional Centers, whereas the difference in apparent prevalence is about 500%. This difference is equivalent to the state-wide difference between Q4 1993 and Q4 2004 (almost the entire 'autism epidemic').

As Paul Choate of CDDS Data Extraction notes, most of the 'epidemic' is confined to several Regional Centers in the greater Los Angeles area, as illustrated by the following figure [courtesy of CDDS]:



The epilepsy argument

Autism has been linked to a seizure liability, and the CDDS data itself shows that the prevalence of epilepsy among autistics is considerably higher to that of the general population. It follows that an environmental trigger capable of producing an epidemic of autism would also result in an epidemic of epilepsy. Surprisingly, we find in the data that the prevalence of epilepsy moves upward at about the same pace as the population in the state of California. Currently, annual growth in number of clients with epilepsy is about 0.6%.

The mental retardation argument

An environmental trigger that results in brain injury or insult should be expected to increase the probability of mental retardation, and thus result in an epidemic of all types of mental retardation. Instead we find that the number of clients with mental retardation is growing at a pace slower than that of the population in the state of California. Cases of profound mental retardation are actually on the decline. (This is explained by misdiagnoses of autism as mental retardation).

Conclusions

The numerical evidence in favor of the notion that an autism epidemic has not occurred at all is clearly overwhelming. Those who claim an epidemic has occurred are apparently not aware of the problem of group inequivalence. This is compounded by fundamental errors in the use of concepts such as incidence and prevalence. In light of these observations, I recommend that all scientific papers that claim to show an epidemic has occurred be retracted immediately.

24 comments:

  1. Joseph,
    You've done a great analysis, but I think you are a little overstating your case to say that you have proven that there is no epidemic. I think you have clearly shown that the numbers from CDDS are flawed, and cannot be used to prove an epidemic.

    Just for the sake of argument, I'd like to make the following case. There is a new disability reflected in these numbers. This disability presents as autism without MR and without epilepsy. It is triggered by urban environments, by something, for example, like a component of smog. After all, autism doesn't have a simple medical test - it's a collection of behaviours. Certainly, it is possible that an environmental trigger has created a genetic mutation that gives rise to a disorder which behaviorally looks like autism but does not have associated MR or epilepsy.

    ReplyDelete
  2. Jennifer,

    You give a good example as to how one might explain the numbers as a true increase in incidence, despite the lack of equivalence. (The argument could also be that there's an epidemic of autistic behaviors not driven by physiological changes).

    I'd point out 2 things:

    1) Note that the proportion of "severe behaviors" is also dropping. This is a behavioral marker. Granted, this is not dropping as much as the physical markers, but without knowing the prevalence of these behaviors in the general population, I can't conclude this is significant.

    2) If the environmental trigger has a liability of epilepsy and mental retardation equal to the general population, you'd expect the 'additional autistics' in any given quarter to not contribute anything in terms of epilepsy or MR in the overall autistic population. It's possible to show they do contribute in terms of epilepsy (in the last quarter, it's something like 3.5% proportion of epilepsy compared to 0.5%-1.0% in the general population). So it doesn't add up. (Mental retardation is volatile in the numbers so I can't make a similar analysis with it).

    3) Your case is theoretical and highly unlikely in practice.

    For these reasons I discount the possibility of a real epidemic.

    ReplyDelete
  3. Very Nice Joseph. Thanks again for all of your excellent work.

    ReplyDelete
  4. Hi Jospeh,
    I think your analysis is very good, but I'd like to point out that when I was teaching for a public school district in California in a classroom with all children who had a diagnosis of autism, only half of them were in the DDS system. The other half were not cleints of any regional center and not even in the DDS system. This doesn't negate anything you have stated, but I just wonder if the CDDS data is the best indicator for incedences, increases in autism...I'd be curious to look at data from school districts to see the number of students with autism from year to year, especially in comparison to the DDS data. That might show some interesting findings...

    ReplyDelete
  5. I was teaching for a public school district in California in a classroom with all children who had a diagnosis of autism, only half of them were in the DDS system. The other half were not cleints of any regional center and not even in the DDS system.

    You're absolutely correct, and this is one of the reasons why CDDS does not recommend using their data to derive prevalence numbers. It probably throws off the numbers somewhat, particularly when it comes to autism. Many of the 'missed' autistics in Fresno perhaps are not 'missed' but simply not registered with CDDS. And it could also be that the proportion of registrations is going up.

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  6. I hate to say this because I don't have a study to back it up, just famiarity with the school districts and RC's, but from what I have seen the proportions do seem to be going up over time. Older children with autism in districts seem to be less proportionally enrolled in the DDS system than younger students. This is why I'd like to see comparative data. I think it would be quite telling. It is hard for students with autism to go undiagnosed in the public school system because teachers are working with them on a regular basis, where DDS does not directly work with poeple with autism. The sytems work very differently...again, why I'd love to see comparative data.

    ReplyDelete
  7. I think there's Department of Education data, which I haven't had a chance to look at yet. I'm not even sure it's publicly available. It probably won't be as detailed as the CDDS data, but it might be interesting to compare and contrast.

    ReplyDelete
  8. Hi Joseph
    I am sorry but, even when you made a big effort, for me these data are not the required to discard or to prove the epidemics.
    The information about comorbilities is scarce, about immune/autoimmune issues is not existent, about genetics/epigenetics, about gastrointestinal issues, and about an enormous amount of published clinical findings in ASD is not considered and other potential biomarkers that are not even mentioned by these.
    How can the severity of the ASD be controlled in time if there are no enough data about?
    Again, we do not know enough about ASD and if the severity of the ASD has changed in time-and then there were new ASD children diagnosed because of the increase of the environmental insult under several forms- to use these data to prove or disprove the epidemics for me. There are no enough information about clinical health status in ASD and the potential of possible combinations made the effort to do this huge and has not been done yet.
    Sincerely
    María Luján

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  9. María,

    This is not really about all possible environmental triggers. It's only about epidemic-causing triggers. The fact is that there's no equivalence as time goes by so a real prevalence increase cannot be assumed. We'd then have to propose that an environmental trigger coincidentally also plays a role. However, we find that only autism changes but not characteristics related to autism. This suggests there's no real trigger at play in any measurable amount. I'd of course like to have more accurate autism markers, like speech development, but the ones available in the data are probably good enough to draw the conclusions I have.

    ReplyDelete
  10. Joseph, thank you for your comment but
    How do we know that the 50 % of today is only 5/10 % of years ago? Or not?
    How do we know that the relative number of the true ASD, the diagnosed and the reported ones under some kind of service has changed in time ? The premise is that the true ASD is the same today and yesterday but I do not see how this can be concluded with this information and no data.
    If there is a shift in several regions to the reported ones and this is partially proven by your analysis and assignable to the numbers increase, what about the true numbers of ASD?

    You say
    However, we find that only autism changes but not characteristics related to autism.
    There is no enough information about. No enough clinical studies. Same behavior can have different neurobiological roots and Different behaviors subtle difference in the same neurobiological roots because of individuality. The problem of comorbilities has not been addressed today, it is in the beginning.
    Thank you for your answer
    MAría Luján

    ReplyDelete
  11. As for the idea that there are only "urban evironments" and pollution in LA... There's horrendous air pollution around Richmond (lots of oil refineries) that's near Oakland (the bay area, northern California). Also the smog in the Sacramento area is heinous, perhaps not as bad as LA, but it's really, really bad. Asthma here is awful.

    If you think about Cure Autism Now starting in LA, the mere presence of wealthy people pushing autism into the public eye could account for the number of extra dxs in LA.

    There could be something special about the pollution in LA, but So. Cal includes much more than LA. San Diego is not particularly polluted, not from what I know of it.

    Joseph your work is great. Thank you, very much.

    ReplyDelete
  12. How do we know that the 50 % of today is only 5/10 % of years ago? Or not?

    We don't. And it seems hard to device a model that explains the drops. However, just with the fact that there's significant inequivalence as time goes by completely switches the burden of proof. That is, there's no reason for me to believe at this point that an epidemic has occurred. The ball is in the court of the epidemic proponents.

    How do we know that the relative number of the true ASD, the diagnosed and the reported ones under some kind of service has changed in time ?

    It doesn't matter in my analysis if the broadening of characteristics is due to broader criteria, more awareness, misdiagnoses, or more CDDS registrations. The key is that severity is going down, hence there's inequivalence, and therefore an epidemic cannot be assumed.

    The premise is that the true ASD is the same today and yesterday but I do not see how this can be concluded with this information and no data.

    If it's not the same, then it's not scientifically correct to say that prevalence of 'it' has increased. A extreme form of this is trying to compare prevalence of autism in the 1970s to prevalence of Asperger's syndrome today. This is a mistaken comparison.

    Since autism is a spectrum that extends into the general population, any broadening of criteria will end up including more people in the criteria: the previously 'almost autistic'. And this can go on until you include the entire population. This is the key to understanding this model.

    If there is a shift in several regions to the reported ones and this is partially proven by your analysis and assignable to the numbers increase, what about the true numbers of ASD?

    We don't know the 'true numbers' of ASD because we'd have to agree on what ASD is. The boundary is obviously fuzzy. If we could compare equivalent groups through time, we'd know if there's a real prevalence increase. However, it's too late to do this. (I'd propose though that researchers can go and compare Westside with Central Valley and figure out what's going on there).

    ReplyDelete
  13. Camille said: "As for the idea that there are only "urban evironments" and pollution in LA... There's horrendous air pollution around Richmond (lots of oil refineries) that's near Oakland (the bay area, northern California). Also the smog in the Sacramento area is heinous, perhaps not as bad as LA, but it's really, really bad. Asthma here is awful. "

    About a year ago, I did something similar to Joseph, except that I looked at the rates of cerebral palsy. I also used the logic that it would be a difficult to miss diagnosis, but I also wanted a diagnosis that was pretty well decoupled from autism. The reason I did this was because I wasn't sure that the populations served by all the regional centers was approximately equal. That the centers serve approximately the same population is an underlying assumption in the interpretation of Joseph's graph of the incidence at each regional center. I calculated the ratio between the # of autism cases and the number of cerebral palsy cases for each Regional Client Center. What amazed me is that there was such a huge variation in this ratio.

    This was done using the March 2005 quarterly data.

    For the entire state, the ratio was 0.80, so slighly less cases of autism than cases of CP. The highest ratios were for

    Frank D. Lanterman (Wiltshire Blvd, LA): 1.72
    Westside (Culver City, also near LA): 1.72
    Harbor Regional (Torrance, also near LA): 1.46
    North LA: 1.38

    and the lowest were

    Central Valley (Fresno, not near LA, with a low population density): 0.35
    Redwood Coast (Northern CA, near Oregon): 0.45

    Camille, what are the names of the regional centers covering Oakland and Sacremento? I still have my little chart, so I can give you the autism/CP ratio.

    ReplyDelete
  14. As for the idea that there are only "urban evironments" and pollution in LA... There's horrendous air pollution around Richmond (lots of oil refineries) that's near Oakland (the bay area, northern California). Also the smog in the Sacramento area is heinous, perhaps not as bad as LA, but it's really, really bad. Asthma here is awful.

    Yes, there's no clear-cut correlation. Sacramento has a low prevalence of CDDS autistics and also one of the lowest of mental retardation.

    If you think about Cure Autism Now starting in LA, the mere presence of wealthy people pushing autism into the public eye could account for the number of extra dxs in LA.

    True, but I'd note that there's not a lot of difference between East LA and West LA. I think it has to do with pediatrician and psychiatrist knowledge and thinking in that particular region.

    There could be something special about the pollution in LA, but So. Cal includes much more than LA. San Diego is not particularly polluted, not from what I know of it.

    Again, I don't think this is the case. You'd expect it to have a strong correlation with mental retardation as well, and it doesn't. Some remote places have a lower prevalence of MR, but this could easily be due to underrreporting. The Inland regional center appears to serve a very sparsely populated area and has a prevalence of MR close that that of the LA area.

    Joseph your work is great. Thank you, very much.

    Thanks.

    ReplyDelete
  15. For the entire state, the ratio was 0.80, so slighly less cases of autism than cases of CP. The highest ratios were for

    Frank D. Lanterman (Wiltshire Blvd, LA): 1.72
    Westside (Culver City, also near LA): 1.72
    Harbor Regional (Torrance, also near LA): 1.46
    North LA: 1.38

    and the lowest were

    Central Valley (Fresno, not near LA, with a low population density): 0.35
    Redwood Coast (Northern CA, near Oregon): 0.45


    You'll find the ratios are roughly the same with epilepsy. This basically says that variation in diagnoses of autism across centers is as orthogonal to epilepsy as it is to cerebral palsy. This does not make sense to me unless the variation is due different definitions of autism.

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  16. I certainly agree with your last point. Joseph, do you know if one doctor at each center vetted the diagnosis? Is there a center-based acceptance criterion that varies from center to center? There are still some puzzling features of my data, for instance that the ratio autism/CP is 1.41, 1.38, and 0.92 in East LA, North LA and South Central LA. The latter data is quite low for something in basically the same geographical area. Is South Central LA less affluent, for instance?

    I'm not from California, and ignorant about these details

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  17. Joseph, do you know if one doctor at each center vetted the diagnosis? Is there a center-based acceptance criterion that varies from center to center?

    I understand they have client evaluations called CDERs. See this document. The data shows which percent was evaluated how soon back. I'm sure there's quite a bit of subjectivity involved in diagnosing autism, and there would have to be a bit of subjectivity involved in diagnosing MR to explain the numbers.

    If you look at these evaluations, it's clear CDDS has more data than shown in their reports. It should be possible for them to determine, for example, if there has been a significant increase in the prevalence of speech delay.

    There are still some puzzling features of my data, for instance that the ratio autism/CP is 1.41, 1.38, and 0.92 in East LA, North LA and South Central LA. The latter data is quite low for something in basically the same geographical area. Is South Central LA less affluent, for instance?

    I'm not sure what the difference might be there. It could just be a peculiarity about that regional center.

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  18. Joseph,

    I find your arguments unpersuasive. Much of what you state as fact is really conjecture. It doesn't take any talent to be a critic.

    ReplyDelete
  19. Much of what you state as fact is really conjecture.

    Some specifics would be nice.

    ReplyDelete
  20. Thanks Joseph for visiting my blog. I only collect information from wherever I can get hold off and sure by all means it's great that you have stumbled on my blog and highlight your point on this issue. Great, another blogger!

    ReplyDelete
  21. Thank you for this blog. I have had to suffer the school system repeatedly diagnosing my late-talking, behaviorally disordered child as autistic simply to get the special education services he needs. The "symptoms" and the diagnosis are continually changing. They've diagnosed him PDD-NOS and Asperger's. I disagree profoundly with both diagnoses. I studied the diagnostic criteria carefully, and he doesn't have all the symptoms. The diagnosticians went so far as to make stuff up to cram him into the diagnostic category. He is very bright, by the way. He taught himself to read, engineers original designs from Legos, is s brilliant artist and a computer whiz.

    I wrote an article based on my own experiences and readings, in an attempt to debunk this over-used diagnosis.

    Thanks again. And to the detractors, I can tell you from first hand experience that Joseph is right on target.

    Jennifer

    ReplyDelete
  22. Thank you for this blog. I have had to suffer the school system repeatedly diagnosing my late-talking, behaviorally disordered child as autistic simply to get the special education services he needs. The "symptoms" and the diagnosis are continually changing. They've diagnosed him PDD-NOS and Asperger's. I disagree profoundly with both diagnoses. I studied the diagnostic criteria carefully, and he doesn't have all the symptoms. The diagnosticians went so far as to make stuff up to cram him into the diagnostic category. He is very bright, by the way. He taught himself to read, engineers original designs from Legos, is s brilliant artist and a computer whiz.

    I wrote an article based on my own experiences and readings, in an attempt to debunk this over-used diagnosis.

    Thanks again. And to the detractors, I can tell you from first hand experience that Joseph is right on target.

    Jennifer

    ReplyDelete
  23. Jennifer,

    Thanks. I don't think ASD is being misdiagnosed most of the time though. It's just that children who are closer to typical are being diagnosed nowadays. I don't necessarily think the diagnoses are mistaken per se, although autism is a construct and its definition subjective.

    BTW, what Thomas Sowell says is not very scientific.

    ReplyDelete
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