Evidence and Causality
If you're interested in the issue of causation a great place to start is page 4 (through 9) of the Institute of Medicine's new report "Adverse Effects of Vaccines: Evidence and Causality". There's lots to consider. For example,support for the Texas Supreme Court's recent determination that plaintiff's will need two well done epi studies to support a claim of general causation:
"The committee does not consider a single epidemiologic study - regardless of how well it is designed, the size of the estimated effect, or the narrowness of the confidence interval - sufficient to merit a weight of 'high' or, in the absence of strong or intermediate mechanistic evidence, sufficient evidence to support a causality conclusion other than 'inadequate to accept or reject a causal relationship.' This requirement might seem overly rigorous to some readers. However, the Agency for Healthcare Research and Quality advises the Evidence-based Practice Centers that it has funded to produce evidence reports on important issues in health care to view an evidence base of a single study with caution (Owens et al., 2010). It does so due to the inability to judge consistency of results, an important contributor to a strength of evidence, because one cannot 'be certain that a single trial, no matter how large or well designed, presents the definitive picture of any particular clinical benefit or harm for a given treatment' (Owens et al., 2010)." (pg. 6)
You'll also get an introduction to the similar yet different GRADE v. EPC approaches to assessing and weighing scientific evidence when making causal judgments. Hopefully, as we've said in the past, courts will one day demand of experts the same sort of transparency in evidence accumulation, assessment and weight assignment that sound science demands.
Along the way you'll note the conspicuous absence of the pronouncements of experts among the things to be determinative in reaching causal judgments. By now that ought not be surprising. As Dr. Steven N. Goodman reported in his journal article "Judgment For Judges: What Traditional Statistics Don't Tell You About Causal Claims" the US Preventive Services Task Force, which is committed to evidence-based medicine, has ranked by reliability the different sorts of evidence that go into making supportable causal judgments. At the top of the list, the strongest sort of evidence, is the well done randomized controlled trial. Then comes the non-randomized controlled trial. Then cohort or case-control studies. Then multiple time series. Dead last, and weakest of all, comes "opinions of respected authorities ..." If science hasn't much use for the mere ipse dixit of credentialed experts it's hard to imagine why the law should hold otherwise.
Anyway, to find out what vaccines cause, and don't cause, and how sound causal judgments are made, this new IOM report is well worth your time.
