A Positive Association found between Autism Prevalence and Childhood Vaccination uptake across the U.S. Population is the latest in a long series of studies purporting to show a link between vaccines and the rise in autism prevalence. Like many of these studies, this one has major flaws. There was a time when I would take the effort to go through such studies in detail. There is enough bad in this one to take so long that I just can’t see taking the effort.
They claim that for every 1% increase in vaccination (defined in a very strange way, as you will see) their study shows that the autism rate (defined in an even stranger way) rises 1.7%.
Look at the title again: A Positive Association found between Autism Prevalence and Childhood Vaccination uptake across the U.S. Population
But, strangely enough, the author doesn’t study autism prevalence. Seriously. The author studies “To determine autism prevalence by U.S. state, the number of 8-year old students classified with either (1) autism or (2) speech or language impairments (speech disorders) was divided by the total number of 8-year-olds in the state.”. Yep, the author lumps autism with SLI. Consider, say, California in 2002 (one of the study years). There were 1,664 8-year-old students receiving services under the disability category “autism”. On the other hand, there were 22,702 8-year-old students in the SLI category. The autism data are basically swamped by the SLI data. Begs the question: what did the analysis show for autism alone? Could it have shown a protective effect of vaccination. Don’t get me wrong, the study isn’t strong enough to show a real association one way or another, but you really got to ask yourself why the author chose to bury autism this way.
In case you are wondering, the autism+SLI “prevalence” for California was about 5% for 8 year olds/3rd graders in 2001 (using 488.633 3rd graders)
Here is the abstract:
The reason for the rapid rise of autism in the United States that began in the 1990s is a mystery. Although individuals probably have a genetic predisposition to develop autism, researchers suspect that one or more environmental triggers are also needed. One of those triggers might be the battery of vaccinations that young children receive. Using regression analysis and controlling for family income and ethnicity, the relationship between the proportion of children who received the recommended vaccines by age 2 years and the prevalence of autism (AUT) or speech or language impairment (SLI) in each U.S. state from 2001 and 2007 was determined. A positive and statistically significant relationship was found: The higher the proportion of children receiving recommended vaccinations, the higher was the prevalence of AUT or SLI. A 1% increase in vaccination was associated with an additional 680 children having AUT or SLI. Neither parental behavior nor access to care affected the results, since vaccination proportions were not significantly related (statistically) to any other disability or to the number of pediatricians in a U.S. state. The results suggest that although mercury has been removed from many vaccines, other culprits may link vaccines to autism. Further study into the relationship between vaccines and autism is warranted.
Here are a few more important points from the paper:
1) They use the “prevalence” of autism or SLI from special education numbers. These data are just not reliable for this sort of work. This has been gone over and over. The best discussion of this is from Jim Laidler in 2005. US Department of Education Data on “Autism” Are Not Reliable for Tracking Autism Prevalence
2) Note that they use cohorts from the mid 1990′s, soon after autism was first added as a special education category. They are pretty much guaranteed that the “prevalence” they calculate will go up.
All they need is to link this to changes in the vaccine uptake. Easily done. The vaccine uptake rate is changing dramatically during the first couple years of the study. For example, Alabama goes from 46 to 76% in two years. Why is that? That brings us to point (3):
3) Here’s a trick bit: the author uses the vaccine schedule from 1995. A brand new vaccine schedule was rolled out and states and pediatricians picked it up over the next couple of years. Of course the vaccine uptake, by this measure, was low at the start.
Yes, they chose a very artificial measure of “vaccine rate” to insure that they had big changes in the “rate” during the study period.
How often do we hear SafeMinds (the author is a member by the way) ask “where’s the study of the vaccinated vs. unvaccinated?” Even when they have the data, they don’t do the comparison. They compare children who got the full 1995 schedule of vaccines vs. children who didn’t (missing one or more vaccines). My guess is there isn’t enough non-vaccinated data to make the study. But, that doesn’t explain why they went ahead with this really bad study.
How about a “too many too soon” study, comparing the total number of vaccines vs. autism rate? Again, not done in this study.
Of course the author is aware of the vaccinated/unvaccinated question. A few quotes from the paper:
A child who missed only one shot was different from a child who was completely unvaccinated, yet in this study both children were classified as not fully vaccinated.
A child who received all but 1 vaccination on time might be different from a child who received no vaccinations, yet both were in the group of children who did not receive timely vaccinations. Had the researchers examined fully vaccinated versus completely unvaccinated children, the results might have been different.
A follow-up study could investigate the prevalence of autism among unvaccinated children. Other children who typically are not vaccinated could be surveyed. These groups include the Amish and children served by Homefirst, a health clinic near Chicago (Eisenstein, 2009), as well as some homeschooled children or younger siblings of children with autism whose parents decided not to vaccinate.
“Eisenstien, 2009″ is a link to the HomeFirst website, which includes unsupported claims. What is the point of a citation to an unsupported claim? For example, in the cited link, Dr. Eisenstein makes the unsupported claim:
“Since 1973, The Homefirst physicians have been offering vaccine choice and awareness Unlike most doctors, the Physicians of Homefirst are honored to serve your family if you give all some or none of the vaccines.
They have virtually no asthma, allergies, ADHD, ADD or Autism in their more then 35,000 un-vaccinated children. “
Where’s the data on how many of their patients have ADD, autism, or the other conditions? Also, I’ve seen the quoted number of “unvaccinated” at Homefirst vary through a very large range.
But back to the actual paper. What does the study claim as a result?
The results suggest that if a given U.S. state has a 1% higher vaccination rate than another U.S. state, then the state with the higher vaccination rate might have, on average, a 1.7% higher prevalence of autism or speech disorders.
Remember, this is using the strange definition of “vaccination rate” is how many children got the full series vs. how many missed any one or more vaccines.
Here you can see their data. Yes, “vaccination rates” and “autism or SLI rates” both go up with time. But it is how they go up that show us how bad this study is:
Take a close look at the vaccination rates for the first two years. That’s when there are the big increases. This is expected because, again, they measuring vaccination rates as the percentage of kids who got the full 1995 schedule, and they start in 1995 when the schedule was just introduced.
The autism/SLI rate, on the other hand, shows a slower, more steady increase (ignoring the noise).
Take a look at table 1. again. Take a look at the first couple of years in, for example, Alabama. The vaccination rate they quote increased from 46% (1995) to 65% (1996), rising again the next year to 76.5% (1997). What did the autism+SLI rate do? It went down.
Recall the result:
Further, if a given U.S. state decreases its vaccination coverage by 1% from one year to the next, prevalence of autism or speech disorders may, on average, fall by 1.7%. If 100% children received this series of vaccinations, the prevalence of autism or speech disorders would be 1.7%
Since the “vaccination rate” went up 20 points (from 46% to 65%), we would expect autism/SLI to go up a lot too: 0.34%, from 4.6% to 4.92%. You can see the same sort of trends in the first two years state by state–big increases in the vaccination rates, small or negative changes in the autism/SLI rates.
It’s only after many years go by that there are notable changes in the autism/SLI rates. Even then it isn’t consistent. Again, look at Alabama. Over the entire study period, the autism/SLI rate went down. Same for the next state on the list, Alaska.
The next state on the list (yes, it’s alphabetical) is one of the “winners” in the study. Autism/SLI rates went up notably over the study period, from 3.8 to 6.2%. But, strangely enough (if you believe the author that is) this didn’t happen for the cohorts which saw the big increases in vaccine rates. A big jump in autism/SLI rate is seen for the last year (a 0.8% jump), but this is for years when the change in vaccination rates was relatively modest.
To put it simply, the result of the study just doesn’t make sense given the data that we (and the referees who cleared this paper) can plainly see. This is a prime example of exactly the sort of paper that really has shown over the years the sort of intellectual dishonesty which has promoted the vaccine-epidemic notion.