What is the probability that D's product causes the type of injury in question?
If D's product does cause the type of injury suffered by P, what is the probability
that it caused P's injury?
P stands for the probability that D's product causes injuries of the type that
P values are usually stated in terms of the probability that the results of
the study could be due to chance, i.e., that the detected harm was not caused
by D's product.
P is a continuum 0 --------------------------> 1
P = .90/.10 90% sure that the result was not due to change - 9 times in 10
P = .5/.5 50% sure - a coin toss (no info about causation)
P = .10/.90 90% sure that the result was due to chance (i.e., that there is
General accepted level of certainty is .95/.05, the results are due to chance
only 1 in 20 times.
For Bendectin, there are 2 issues: Are we 95% certain that Bendectin causes
any birth defects.
Then, what is the relative risk, i.e., what is the chance that Bendectin caused
the P's birth defect.
The P's baby had a birth defect and there was no other obvious cause: how can
it be that Bendectin did not cause the birth defect?
How common are birth defects?
____% of babies have a birth defect of any type?
____% of babies have a serious birth defect
____% of pregnancies end in miscarriage
5,000,000 births a year
30,000,000 women took Bendectin, ____ babies with serious birth defects are
Animal studies are not predictive of human birth defects ‑ Thalidomide.
What was Thalidomide and why was it given?
What did it cause?
Phocomelia is a rare defect, , but seen in a bunch of Thalidomide cases.
What is DES and why was it given?
DES causes clear cell adenoma
How long does it take?
How common is it?
How did we ever discover the linkage?
Low background + unusual injury + good reporting
Contrast with Agent Orange
_______________ men and women, mostly men.
Nature of the injury?
Expected background level of birth defects?
_____% background rate X ____________ kids = ?
Cancers ‑ ____% expected X __ persons at risk = ?
How many cases of Agent Orange injuries would there need to be for them to
Is there credible evidence that Agent Orange causes injuries?
Why is the VA paying?
The key value is the relative risk that D's product caused P's injuries.
Relative risk is the % increase in the number of injuries (over background)
due to D's product.
A relative risk of 1 (100%) means that the product does not cause the injury.
A relative risk of 2 (200%) means that the product doubles the number of expected
Some courts equated a relative risk of 2 with the negligence standard of preponderance
of the evidence.
What does a relative risk of .5 imply?
What should be the relative risk of clear cell adenoma from DES?
Relative risk of Thalidomide induced injuries?
Assume that a new anti‑nausea drug, Vomital, causes a generalized increase
in serious birth defects (but no unusual birth defects) of 100 per 1,000,000
What is the relative risk of a Vomital induced birth defect?
Some courts use 2 as the minimum for caustion because of more probable than
How many birth defects would Vomital have to cause to get to RR 2?
How sure are we of the relative risk?
Confidence Intervals for Vomital (graph)
95% =6-2.7 / 90% =9-2.0 / 80%=1.6-1.8 / 50%=1.66
Key factors: relative risk and size of study group
Why is Thalidomide ideal?
What about DES ‑ latency is a problem
What about Vomital?
How many women would you have to study to establish the causation to P = .05?
Study design is critical.
Must carefully identify the population at risk
Must carefully identify the control population
Must be matched
Must identify the condition of interest
Retrospective analysis of data is a problem
Confounded by correlation with smoking
De caf causes cancer
Confounded by people with health problems off high lead
Wine drinking reduces heart disease?
Trolling for correlations
Lab tests are 95% confidence level
In 20 tests you would expect 1 false positive.
At 95%, 2 of you could be murders.
Criminal v. Civil Standards
Step function versus smooth, versus hyperbolic
Graph with long tail buried in background
Step function with threshold above routine exposure values.
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