Confidence in court: A delicate balance
In her News In Depth “Europe’s top court alarms vaccine experts” (30 June, p. 1320), G. Vogel discusses the European Court of Justice’s finding that a plaintiff can present circumstantial evidence that a vaccine caused a disease, even if scientific studies have been inconclusive. The implications of this decision depend on the standard of certainty applied by courts. Scientists typically apply a 95% confidence criterion. A lower bar for evidence in court may not constitute an absence of scientific evidence. Conservatism in science protects the knowledge base from errors introduced by inadequate stringency. Public health professionals, however, must simultaneously be conservative in protecting life and health. This may require considering associations, such as cancer clusters or vaccine side effects, that are probably causal, or even associations that only might be causal. For example, public health professionals should not overlook a cluster of cancer cases associated with a carcinogen, or an adverse clinical effect associated with a vaccine, if the statistical confidence level is only 90%. Courts—including judges, juries,
LETTERS
attorneys, and the expert scientists and public health professionals who testify— therefore must balance opposing needs: rejecting unscientific or antiscientific claims versus accepting claims of injury, if probable, even if not proved to a scientific degree of certainty.
In statistics, the conflict is between type land type 2 errors. In a type 1 error, a true null hypothesis is rejected (for example,
a real cancer cluster or vaccine side effect
is missed). In a type 2 error, a false null hypothesis is accepted (for example, a statistical fluke is interpreted as a real cancer cluster or a real vaccine side effect). In testing whether an alleged cause of injury “probably” is the actual cause, courts should adhere to scientific principles, even if they apply a lower statistical confidence standard.
Robert Michaels RAM TRAC Corporation, Schenectady, NY 12309, USA. Email: ram@ramtrac.com
10.1126 /science.aao3967
Publication citation
Michaels, RA. Confidence in courts: a delicate balance. Science Magazine, 357(6353):764, Letters, doi: 10.1126/science.aao3967, 25 August 2017;