In my last post I wrote about heuristic biases that lead to wrong and even dangerous conclusions. The one bias that runs rampant in media reporting of science, (Gary Schweitzer -- who claims he is objective -- is the worst offender) is relying upon single studies with small sample sizes that claim statistical significance (internal validity) to make a sweeping judgement about the dangers of chemicals, soda, medicines, etc.
This week a single study, "Serum Vaccine Antibody Concentrations in Children Exposed to Perfluorinated Compounds" was published in JAMA http://jama.ama-assn.org/content/307/4/391 this week claiming that "elevated exposures to PFCs were associated with reduced humoral immune response to routine childhood immunizations in children aged 5 and 7 years. " The research is the only study to look at PFC levels over time in humans. The handful of other studies have only looked at the relationship betwee immune suppression in rats at human PFC levels. Blood samples in this study were taken to measure PFC levels in maternal pregnancy serums and then at age of 5 and 7. There was no regular monitoring of serum levels from birth to age 5 or 7 nor from age 5 to 7. The group was not compared to controls with different serum levels and antibody response. So the results are just as likely to be random as they are to be suggestive.
But that didn't stop JAMA or media outlets to sound the alarm using the heuristic of representativeness and small sample sizes to draw conclusions about probablities that are not supported by the evidence:
Chemical Contaminants Linked To Low Immune Response To Vaccines MedicalNewsToday
Chemicals linked to lower vaccine response in children AFP
However, Liz Szabo at USAToday provides the most balanced evaluation of the study and frames the coverage by calling to the limited sample size and the absence of causality.
http://yourlife.usatoday.com/health/story/2012-01-24/Chemical-exposure-may-compromise-vaccine-response/52774114/1
Chemical exposure may compromise vaccine response
"Children exposed to chemicals called PFCs — used in some non-stick cookware, stain-resistant coatings, fast-food packaging and microwave popcorn bags — have a reduced response to vaccines, raising the possibility that the compounds could prevent children from being adequately protected against disease, a new study shows..."
She goes on to cite Paul Offit, a straight shooter and great guy (even though he is a Phillies fan) and to point out that PFC levels are decreasing:
"Grandjean acknowledges that his study's design doesn't definitively prove that PFCs compromise children's vaccine response. It's possible that something else affected their response, says Paul Offit, chief of infectious disease at Children's Hospital of Philadelphia. For example, it would help to know if children with higher PFC levels have any basic immune system problems, independent of vaccines.
The EPA and chemical industry phased out U.S. production of one of these compounds, PFOS, or perfluorooctane sulfonic acid, in 2002. Since then, blood tests show that exposure to this chemical have declined, Grandjean says. Manufacturers are in the process of phasing out another major compound, called PFOA, or perfluorooctanoic acid.
"But other PFCs may be increasing," Grandjean says. "PFOS is now produced in large amounts in China."
In the past, Ms. Szabo has also been relentless in her coverage about the science behind the public health benefits of vaccines. Great work then and now.
This week a single study, "Serum Vaccine Antibody Concentrations in Children Exposed to Perfluorinated Compounds" was published in JAMA http://jama.ama-assn.org/content/307/4/391 this week claiming that "elevated exposures to PFCs were associated with reduced humoral immune response to routine childhood immunizations in children aged 5 and 7 years. " The research is the only study to look at PFC levels over time in humans. The handful of other studies have only looked at the relationship betwee immune suppression in rats at human PFC levels. Blood samples in this study were taken to measure PFC levels in maternal pregnancy serums and then at age of 5 and 7. There was no regular monitoring of serum levels from birth to age 5 or 7 nor from age 5 to 7. The group was not compared to controls with different serum levels and antibody response. So the results are just as likely to be random as they are to be suggestive.
But that didn't stop JAMA or media outlets to sound the alarm using the heuristic of representativeness and small sample sizes to draw conclusions about probablities that are not supported by the evidence:
Chemical Contaminants Linked To Low Immune Response To Vaccines MedicalNewsToday
Chemicals linked to lower vaccine response in children AFP
Vaccine effectiveness reduced by common environmental toxin . Boston Globe
However, Liz Szabo at USAToday provides the most balanced evaluation of the study and frames the coverage by calling to the limited sample size and the absence of causality.
http://yourlife.usatoday.com/health/story/2012-01-24/Chemical-exposure-may-compromise-vaccine-response/52774114/1
Chemical exposure may compromise vaccine response
"Children exposed to chemicals called PFCs — used in some non-stick cookware, stain-resistant coatings, fast-food packaging and microwave popcorn bags — have a reduced response to vaccines, raising the possibility that the compounds could prevent children from being adequately protected against disease, a new study shows..."
She goes on to cite Paul Offit, a straight shooter and great guy (even though he is a Phillies fan) and to point out that PFC levels are decreasing:
"Grandjean acknowledges that his study's design doesn't definitively prove that PFCs compromise children's vaccine response. It's possible that something else affected their response, says Paul Offit, chief of infectious disease at Children's Hospital of Philadelphia. For example, it would help to know if children with higher PFC levels have any basic immune system problems, independent of vaccines.
The EPA and chemical industry phased out U.S. production of one of these compounds, PFOS, or perfluorooctane sulfonic acid, in 2002. Since then, blood tests show that exposure to this chemical have declined, Grandjean says. Manufacturers are in the process of phasing out another major compound, called PFOA, or perfluorooctanoic acid.
"But other PFCs may be increasing," Grandjean says. "PFOS is now produced in large amounts in China."
In the past, Ms. Szabo has also been relentless in her coverage about the science behind the public health benefits of vaccines. Great work then and now.
More vaccine coverage:
Continuous coverage by health reporter Liz Szabo on the myths and benefits of vaccines.
- Common myths about vaccines
- Measles returns as some parents refuse vaccines
- Parents describe pain of losing children to vaccine-preventable diseases
- Adult vaccines can hold down health costs
- More kids skip school shots in 8 states
