About the SA Blog Network



Opinion, arguments & analyses from the editors of Scientific American
Observations HomeAboutContact

Autism and mammography: Two stories of statistical confusion

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint

whiteboard with figures on itDENVER—There was substantial public outcry last year when new recommendations for mammograms came out suggesting that women could wait until age 50 to start breast cancer screening—and then only get screened every other year. Figures in support of the new policy were bandied about in the news and in doctors’ offices, regarding lives saved from breast cancer (eight women per 1,000) and false positive results (2,250 per 1,000 women). But in spite of the new recommendations, many women and clinicians were unsure about forgoing the additional screenings called for under the old policy if there was hope of saving even one life.

The U.S. Preventive Services Task Force, which made the recommendations (that women ages 50 to 69 get mammograms every other year), based their decision on analyses of eight randomized controlled trials. Although eight might not sound like a lot of studies for a disease that affects so many women (about one in eight will be diagnosed with breast cancer at some point in her lifetime), when compared with the larger literature on disease screening, "that is an embarrassment of randomized controlled trials," Ned Calonge, of the Colorado Department of Public Health and Environment, said here Tuesday at the American Public Health Association annual meeting. And by embarrassment, he means "a plethora of data," he explained.

The one in eight statistic can be confusing, Calonge said, because most women who get breast cancer do not die from it. In fact, from a baseline of 1,000 women who never have a single mammogram, 30 will die from breast cancer (if followed from age 40 onward). And that, Calonge pointed out, is already a small number to try to whittle down. 
If screening is bumped from biannual to annual for women starting at age 40, it would save almost one additional breast cancer death per 1,000 women, he noted.

The reason that more screening earlier does not translate into many more lives saved, which has been borne out through studies and meta-analyses, is that "as you get older, the test itself gets better," Calonge said. The shift in breast composition results in fewer false positives as women reach their 60s, which is "when you really need to push screening—because it becomes a very good test at that age."

And with more tests comes more potential for harm caused by stress from false positive and unnecessary invasive procedures. Just doubling the number of mammograms performed, Calonge noted, would also double the number of false positives and unnecessary biopsies. (One thousand women getting screened every year between the ages of 40 and 69 will produce some 2,250 false positive results and 158 unnecessary biopsies over those 30,000 mammograms.)

The bottom line, he noted, is what so many public health experts, physicians and journalists offered last November: Women in their 40s "should weigh the risks and benefits" and talk with their doctors about whether they want to start screening for breast cancer early, Calonge said.

Misapprehension of statistics and scientific process has been even more apparent in the misunderstandings surrounding vaccines and the onset of autism.

Given the age at which children receive immunizations and that at which many cases of regressional autism manifest themselves (in which a seemingly normally developing child suddenly loses much of the ability to communicate as well as other acquired functions), "by chance alone" there will be a lot of children who regress at some point after getting their scheduled vaccines, Daniel Salmon, a vaccine safety specialist at the U.S. Department of Health and Human Services (HHS), said here on Tuesday.

As he pointed out, however, "temporality is insufficient to show causality." But underlying—and perhaps highlighted by—this "logical fallacy," he explained, is a frequent hang-up of science communication: the devil is in the details, and the details can be complicated (and not too catchy) to explain.

When Jenny McCarthy, an advocate of the vaccine-autism link, goes on CNN’s Larry King Live and says, "’Vaccines cause autism,’ that’s a very clear, simple message," Salmon noted.

Most respected scientific bodies, however, are not prone to such blanket statements. In a 2004 report essentially dismissing the assertion that vaccines cause autism, the Institute of Medicine (IOM) was notably more measured than McCarthy, concluding that "based on this body of evidence, the committee concludes that the evidence favors a rejection of a causal relationship between thimerosal-containing vaccines and autism…" The report also included appropriate caveats about the limitations of the available data, which many in the anti-vaccine community took as evidence that there was in fact evidence for a link.

Much of the rallying around vaccines (and/or their thimerosal additive) and autism has centered on powerful stories about children who developed regressional autism shortly after receiving immunization. But "the anecdote is not data—though it often seems that way" in the public debate about autism’s causes, Salmon said. And likewise, correlations are not the same as causation. All kinds of outside factors, from recommended vaccines to the size of the internet, can be plotted to match the rising curve of autism rates, he noted, underscoring that "I’m not suggesting that the internet causes autism."

Despite the dearth of durable data showing that vaccines can induce autism, some 25 percent of parents in the U.S. still believe them to be a possible cause (a statistic which is "really quite remarkable," Salmon said with a bit of distress).

And the cautious nature of science is unlikely to be able to dispel belief in the link any time soon. "It’s exceedingly difficult—and some in epidemiology would say impossible—to prove a negative," Salmon said.

Image credit: Flickr

Rights & Permissions

Comments 23 Comments

Add Comment
  1. 1. amdachel 7:47 pm 11/10/2010

    Katherine Harmon presents a false and misleading view of the controversy over vaccines and autism. While she can give us lots of statistics on breast cancer, she fails to mention even one figure about autism. She doesn’t say that in the 1970s, autism affected one in 10,000 kids and today everyone knows someone with an autistic child because it strikes ONE PERCENT of children and almost TWO PERCENT of boys. Harmon slams the autism community for daring to question vaccines. The thousands of parents who report that their children were healthy and normally developing until they received routine vaccinations are simply wrong—all the studies show no link. She doesn’t note that every study used by health officials has been shown to be tied to the vaccine makers. Hundreds of employees at Centers for Disease Control and Prevention have waivers because of direct financial ties to the pharmaceutical industry. The last director of the CDC, Julie Gerberding, a long-time denier of any link, is now the head of the vaccine division at Merck Pharma.

    Daniel Salmon from HHS calls it just a coincidence when kids regress into autism after being vaccinated, but we should remember that the CDC, which runs the vaccine program, is under this Dept. Salmon can be expected to defend the safety of vaccines.

    THE STUDY THAT WOULD END THE CONTROVERSY TOMORROW HAS NEVER BEEN DONE. No official has ever called for a study comparing the autism rate in kids who’ve been fully vaccinated with kids who’ve never received any vaccines. If one percent of unvaccinated kids also have autism, then the proof would be there for all to see. No one has ever wanted to see this research done. We seriously need to ask why.

    Anne Dachel, Media editor: Age of Autism

    Link to this
  2. 2. jtdwyer 9:40 pm 11/10/2010

    Wasn’t the supposed link between vaccination and autism not only coincidental but the product of fraudulent research? As I vaguely recall, in the 1970s only severely affected children would have been diagnosed by a medical community that had little knowledge of autism. Today, as I understand, diagnosis of a now broadly expanded group of symptoms is commonly made by not just psychiatrists and psychologists but through referrals by a large community of social welfare workers.

    You seem to me to be personally heavily invested in the vaccination causation hypothesis, once actively supported by large, misled parental groups.

    Link to this
  3. 3. maurinemeleck 9:43 pm 11/10/2010

    Vaccines don’t cause autism is also a very clear and simple message. What do these 2 people suggest causes this regression. I bet they have not one response to the reason that almost 2 per cent of young boys are on the autism spectrum. The "scientific" studies they continue to refer to are not any more measured than McCarthy’s statements because the "so-called" studies are done by those with a stake in the results i.e a study that shows a link between autism and vaccines. We need that independent study of vax vs unvaxed children. Why is the government afraid of this?
    By the way, jenny McCarthy is still Jenny McCarthy; she is not the former Jenny McCarthy unless I have missed something in the last 12 hours. This article is so biased and "unscientific" and lacking durable data that I suspect 75 per cent of parents would use it to pack their garbage.

    Link to this
  4. 4. maurinemeleck 9:53 pm 11/10/2010

    still actively supported by the even larger autism community. We are all heavily invested because we all have heavily sick children suffering from oxidative stress, immune dysfunction, inflammatory bowel disease, regressive encephalopathy. Your recall is certainly vague because the huge increase in autism can be charted evenly alongside the huge increase in the number of unsafe vaccines given starting in the early 1990′s.

    Link to this
  5. 5. jbairddo 10:46 pm 11/10/2010

    Why is there any argument about this at all. thimerosal contains mercury, second in toxicity to plutonium. There is no safe limit-end of story. Even if 99% is excreted, is 1% safe? H**L NO. You can ignore all the stats you want about the increase in asthma and other inflammatory diseases, but doesn’t change the reality. Dachel is correct, the study to end this hasn’t been done, chiefly because kids who end up healthier after not being vaccinated would be really bad for business.

    Link to this
  6. 6. sjn 11:51 pm 11/10/2010

    The lack of depth in current Sci Am articles continues to be disturbing.
    For example, regarding the autism/thimerosal link, there is no reference to the extensive data showing that autism rates continued to rise after thimerosal was removed from vaccines (example, in Denmark, where thimerosal was removed from vaccines over a decade ago, with no impact on autism rates. I believe the case is the same in Canada).
    This is not to say that mercury exposure is "good", or in any way to "defend" mercury exposure. But if you really want to understand the cause(s) of the range of autistic behaviors its time to move past the vaccine/thimerosal debate to more useful avenues.
    These short/weak/dumbed down Sci Am pieces do little to encourage or build scientific literacy about crucial topics of public concern

    Link to this
  7. 7. popcares 7:49 am 11/11/2010

    "And the cautious nature of science is unlikely to be able to dispel belief in the link any time soon. "It’s exceedingly difficult–and some in epidemiology would say impossible–to prove a negative," Salmon said."

    Silly me..I would have thought a prestigious "science" magazine would already know the serious limitations of "epidemiology" .. such as .. it’s well recognized flaw of being unreliable because it is too easily maniuplated to reach a predetermined conclusion.

    Silly me…I would have thought this article would have at least made mention of the numerous scientifically independent "toxicological" studies done on various species .. such as .. guinea pigs, rats, mice and even primates (monkeys) .. that ALL clearly demonstrate the delayed or otherwise impaired neurological development "caused" by thimerosal (among other toxic substances .. such as .. alluminum) containing vaccines.

    Instead of educating your readers about the severe limitation of "epidemiological" studies .. you really should be focusing their attention on the "toxicological" studies already done.

    Link to this
  8. 8. maurinemeleck 8:32 am 11/11/2010

    Sorry SJN-thimerosal was not completely removed and it was also added to the flu shot-recommended for almost everyone—way back in 2004(including pregnant women) Please get your facts correct.

    Link to this
  9. 9. JohnDanStone 11:13 am 11/11/2010

    What a sorry state scientific journalism is in, Ms Harmon. Thimerosal, you forget to mention, is 50% mercury by weight! And it isn’t awfully good for you. The amount of mercury in a thimerosal containing vaccine is typically 250 the hazard level for toxic waste.

    Link to this
  10. 10. ssm1959 1:14 pm 11/11/2010

    A large section of the populace had been led to believe that the "no risk" alternative actually exists. How you move people beyond that is difficult. Unfortunately it may take bad experience to drive home the message. Move away from the fussy issue that is autism and move to a more concrete issue related to vaccination: approximately 1 in 250 thousand will suffer severe complications or die from allergic and other reactions to vaccines. A population used to seeing a significant numbers die each year from preventable disease will gladly accept this remote risk of vaccine associate mortality. Populations like the US where several generations have never seen epidemic disease lose this perspective and figure that all they have to fear is the vaccine. Recent outbreaks of pertussis are warning signs that this biologically short "Camelot" we in the west have enjoyed being free from epidemic disease is at risk of coming to a close. As the number of non-vaccinated increases in our culture we may get the needed education right up front and in a very personal way. It would be far better to make inroads with the fear based faction of our country before it is too late.

    Link to this
  11. 11. jtdwyer 2:27 pm 11/11/2010

    That you have severely affected children doesn’t justify your being emotionally invested in the now discredited research that originally indicated vaccines as the causal factor in the incidence of autism.

    I myself not only have progeny that are (thankfully mildly) affected with ASD, but I’m a 60 year old undiagnosed survivor, along with most of my other male relatives. I suggest that the vaccines of the 1990s did not produce my symptoms nor those of my family, since Asperger syndrome was not an officially recognized diagnosis until 1992.

    What you failed to grasp from this article is that statistical correlation does not establish any casual relationship. There are innumerable environmental factors that can be correlated to the increasing incidence of ASD diagnosis since the 1990s, but there are more likely candidate causation factors.

    Link to this
  12. 12. JohnDanStone 4:18 pm 11/11/2010

    Unfortunately, the problem with the recurrence of whooping cough insofar as it isn’t simply an artefact of doctors recognising the symptoms in a disease which was formerly supposed to have been eradicated (and can be confused with several others) is that vaccination doesn’t work very well. Scratch the surface and there is a lot of literature on this. But it is indicative that we need more and more pertussis shots and more and more measles shots to stay in the same place. This is a story about the failure of the method rather than about the few who abstain.

    Until governments and the medical profession actively monitor the affects of vaccine as keenly as they search down cases of infectious diseases like whooping cough or measles we will not have any meaningful comparison. A 2006 NIH study showed that about 1 in 17 infants on receipt of MMR ran a tempertature of 39.5C or more, but there was no long term follow up to see how they fared.

    VAERS has 345,000 events reported:

    but you have to bear in mind that with passive surveillance as in this case under reporting is likely to be 90-99%. Also, infant mortality had largely collapsed in the developed due to better living condition (sanitation, nutrition) before the big vaccination programmes and certainly the heavy schedules of the last two decades.

    On the other hand we now have unprecedented NDDs, allergies, diabetes, obesity and health officials steadfastly looking in the opposite direction whenever the possibility of a vaccine connection is mentioned. It is simply not done, not good manners.

    Link to this
  13. 13. base651 4:32 pm 11/11/2010

    As the father of an autistic child, a previous employee of a global vaccine manufacturer and post grad in biological sciences, I’ve followed the debate re: vaccines and autism with a ‘high’ degree of interest. The following comments may help dispel some misunderstandings or at least provide a counter-position to some of the above.
    Firstly, there is a wealth of data looking at the rates of autism in vaccinated and unvaccinated children. A retrospective Danish study of over 500,000 children showed no signficant differences in rates between the 2 groups. You can find this exact citation via pubmed but its NEngJMed 2002.
    Secondly, an international group, the autism genome project published in Nature, Pinto et al 2010 showed a much higher rate of CNV’s in autistic children vs controls when looking at genes linked with GTPase and neuronal development (I think that’s a fair summary but I have lost the original paper-please correct me).This suggests that the brain doesn’t develop like neurotypicals. Whilst not suggested in this article many would believe this occurs in utero. Further evidence of a genetic link comes from the familial rates between parents, siblings and an affected child.
    Thirdly, the increase in autism could be related in part to improved detection (note it wasn’t a disorder 100 years ago!). In this respect better detection goes a long way (but not fully) to explaining the rise in many diseases including some types of cancer.
    Finally, early use of eye tracking and follow-up of babies thought to be autistic and subsequently being diagnosed is now suggestive that stereotypical behaviours are occuring prior to the age of vaccination (this is still tenuous and the data weak but prompts other areas of investigation).
    Personally, when someone criticises vaccination, which is their right and perogative it may be helpful to understand their familiarity with some basic life sciences, epidemiology and neonatal development. Why is it that all national paediatric socities endorse vaccination (please highlight one if I am mistaken)? For those that have concerns about mercury in vaccines the amount is nominal. Take some time and see how this compares to that found in dietary fish, differentiate between the ethyl and methyl compounds, the amounts ingested and contrast with the mercury poisoning in Japan from the 60′s-famous case studies. Poor science, scaremongering and fear are common threads to the anti -vaccination lobby. When you watch a child die from menigococcal septicamia (when a vaccine was available, you feel sick)

    Link to this
  14. 14. JohnDanStone 4:34 pm 11/11/2010


    Why is it that you are able to to suggest that Maurine Meleck is emotionally invested and you are not. On the Olmsted/Blaxill model you are quite young enough to have had the chemical exposures that they are talking about. Incidentally, people knew about the autistic continuum before the current definitions and jargon. I remember being told by a mental health official c.1971 that he had just been reading a biography of Beethoven and he reckoned he was autistic (we now know Beethoven suffered from lead toxicity).

    Link to this
  15. 15. jtdwyer 6:14 pm 11/11/2010

    I made no remark regarding my emotional investment but provided plenty of evidence for you. My complaint was that Maurine Meleck had attacked this article about statistical misrepresentations of causality solely on the basis of vaccine research that has now been widely discredited. It was her stated association with

    Perhaps I confused Maurine Meleck’s reply to my comment to Anne Dachel, Media editor: Age of Autism. However, that all three of us have some vested interest in ASD does not justify supporting invalid research while dismissing more promising causations.

    It does ASD sufferers a disservice to focus in on what may be at most a minor contributing factor simply because it had garnered widespread public support as a result of the self promotional activities of a probable charlatan.

    By the way, I think that in the 1970s it was mostly the Beethovens and Newtons of history that were being diagnosed rather than any but the most profoundly affected children of the U.S.

    It seems to me as a child of the 1950s that more children were diagnosed with polio than autism. In most of the small towns where the majority of the population resided, there wasn’t much screening of children for ASD symptoms.

    Link to this
  16. 16. jtdwyer 6:17 pm 11/11/2010

    base651 – Thanks for your excellent, insightful and informative comments.

    Link to this
  17. 17. JohnDanStone 7:50 pm 11/11/2010


    The point is that it is a gratuitous insult to suggest that Maurine Meleck has an emotional investment in the vaccine theory. She may have very good reasons for believing what she does, or possibly – if you subscribed to the ideology of bio-diversity, or felt guilty about vaccinating your children it might be equally true about you. It doesn’t help. Nor does citing received opinions without discussing the science.

    For example, the Danish paper base651 was heavily criticised by Cochrane:

    "The follow up of diagnostic records ends one year (31 Dec 1999) after the last day of admission to the cohort. Because of the length of time from birth to diagnosis, it becomes increasingly unlikely that those born later in the cohort could have a diagnosis" (Re: Madsen 2002)

    Indeed, the Danish studies have rightly fallen under a cloud since the man who set them up between the CDC and the Danish State vaccine manufacturer absconded with $2m, although the police seem to have been slow to investigate.

    In fact, the entire IOM review of which the Madsen study was part was tainted, as revealed in the minutes of the closed meeting 3 years before it reported.

    Dr. McCormick states, “we are not ever going to come down that it is a true side effect,” before the committee had considered any evidence [page 97]. Also noting the CDC “wants us to declare, well, these things are pretty safe on a population basis.” [page 33]. While her colleague Dr Stratton remarks “the point of no return, the line we will not cross in public policy is to pull the vaccine, change the schedule. We could say it is time to revisit this but we will never recommend that level. Even recommending research is recommendations for policy. We wouldn’t say compensate, we wouldn’t say pull the vaccine, we wouldn’t say stop the program.”[page 74]

    So, for safety sake studies are commissioned from the CDC or associated institions in Denmark and the UK.

    This, of course, is the way modern science is conducted

    The Pinto study is the ultimate demonstration of the near irrelevance of gene studies to the autism question. The variations if they are remotely significant may well be environmentally induced.

    They cast the net ever more widely looking for ever more minute statistic associations.

    Link to this
  18. 18. jtdwyer 8:59 pm 11/11/2010

    Perhaps my inconsideration for the emotional needs of others in perpetuating the established vaccine causation myth was intentional, determined to be necessary to produce the desired effect, or perhaps it was symptomatic.

    I am sorry for all who suffer in any way, but I try to help as best I can. There has been a vaccine causation myth perpetrated on the population of ASD sufferers and their families. The cold hard truth is that, as attractive as that myth is in relieving parental feelings of guilt, it is not likely a useful solution to reducing the incidence of diagnosed ASD.

    I make no apologies for expressing my somewhat aberrant opinions: in my experience they can be useful and effective.

    Link to this
  19. 19. JohnDanStone 3:36 am 11/12/2010

    I take your point to some degree about failure to detect Asperger cases in earlier epochs however there seems to be a problem also with detecting lower continuum cases in the adult population in sufficients number even now to support a theory of static incidence. With all our modern day awareness we are not retrieving the cases.

    Also, I know that c.1999 in our local school population (a London borough)the same services that had detected over 100 cases in primary education were finding not more than about one a year at secondary level (but these problems don’t get easier at secondary level). In 2010 we have 52 coming through to adulthood and many of these are very disabled, couldn’t be missed in a million years. This is likely to be repeated for several years to come.

    You talk about the vaccine causation myth: I talk about the vaccine safety myth and I am prepared to talk in specifics not just the generalisations of received opinion as once against manifested by this ill-researched and unquestioning article.

    Link to this
  20. 20. louisejulia 8:55 am 11/12/2010

    Firstly, may I point out that according to the WHO, worldwide vaccination has prevented an estimated 4.3 million deaths from measles alone since 2000. As others have quite rightly pointed out, in the developed world we are now thankfully removed from seeing first hand the devastation these diseases can cause. Sadly, in 2006, in the midst of lower vaccination uptake after the MMR scare, the UK saw it’s first measles death for 14 years, in an immunosuppressed teenager.

    This leads me to my second point, which is the danger of these ‘normal’ childhood illnesses to immunosuppressed children, of whom there are many, whether or not they have received their own immunisations. Here in the UK, one in approximately every 500 children develops some form of cancer by the age of 14 (data from National Registry of Childhood Tumours) the treatment of which leaves them seriously immunosuppressed. I will admit I am not unbiased here, as the parent of a very brave little girl fighting her own battle against leukaemia. She, and the many other brave kids like her very much depend upon a good level of community cover to protect her from infections her compromised immune system cannot fight.

    Cancer is of course by no means the only condition causing immunosuppression; any child receiving immunosuppressive treatment for rheumatoid arthritis or Crohn’s disease for example, or with HIV/AIDS also suffers the same issues. Many other children are also at increased risk from these illnesses including those with lung or heart disease – the list goes on and on.

    You may say "but what is the benefit of herd immunity to my normal child?". Even if this self-centred viewpoint is accepted, it misses the point that your child may be normal now, as mine was not that long ago, but they may not be so in six months time.

    For the record, I do believe as much attention as possible should be paid to vaccine safety issues, such as using the most biologically inert stabilisers and preservatives and increased training of staff to spot and treat adverse reactions. I myself carefully checked to make sure my child was receiving thiomersal free preparations, just in case. I had, however, ensured that she received her full quota of childhood vaccinations before her illness and I continue to do so, for her sake and that of others. What a tragedy it would be for another child to lose their life not because they could not fight their own challenging illness, but because they could not fight the ‘minor’ illness of another child that should never have happened in the first place.

    Link to this
  21. 21. JohnDanStone 10:47 am 11/12/2010

    The global decline in flu mortality since 2000 is an artefact of reporting.

    Hilary Butler commented in BMJ Rapid Responses:

    ‘Last year, WHO (2) stated that measles mortality in Africa had slashed the death rate from measles by 91% since 2000. This 91% is an artifact figure, because before 2000, measles in Africa was "estimated", while after 2000, notifications were only accepted after being laboratory proven. In 2000, WHO implemented a system of laboratories (3) specifically to diagnose measles, and provide the laboratory confirmed cases which are now the basis of WHO data.

    ‘Look at pages 2, and 14. On page 14, 14,185 cases were reported in 2006, but after blood testing, 9,764 were "discarded". That’s an immediate 69% drop in cases, because they are no longer relying on doctor’s eyes.

    ‘On page 2, of 14,185 cases, 3,257 were accepted, leaving a balance of 10,928 discarded measles cases which equals 77% which were NOT measles after being blood tested, but which would have been accepted on the pre- 2000 measles notification system. Comparing data from laboratory-confirmed blood tests after 2000, with pre-2000 guessing, and then claiming a 91% decline, is not a valid scientific comparison.’

    Similar strictures apply to reporting of the incidence of measles in the UK. It will come as no surprise that the UK authorities set out to track down and confirm every case of measles with Andrew Wakefield up in front of the GMC but prior to 2000 there was virtually no lab testing and no confirmed cases. The only way for confirmed cases to go was up!

    The figures a just twisted to suit the policy.

    Link to this
  22. 22. JohnDanStone 11:10 am 11/12/2010

    The figures are just twisted to suit the policy.

    Link to this
  23. 23. Gramj 2:00 pm 01/6/2011

    The statistics on breast cancer are really helpful, but I agree there needs to be more evidence to support the views concerning autism. There are so many unknown side effects to substances such as lead toxicity or other ingredients in vaccines. If this topic interests you further, the website would be good to check out.

    Link to this

Add a Comment
You must sign in or register as a member to submit a comment.

More from Scientific American

Email this Article