Evidence

[[File:Evidence.png|right|165px|thumb|A Rough Guide to Types of Scientific Evidence<br/><small>([https://rationalwiki.org/w/images/6/63/Evidence.png Click to enlarge])</small>]]{{Philosophyscience}}
'''Evidence''' is an observation, [[fact]], or document that tends to make more likely the conclusion which the evidence is offered to prove. When offered as [[proof]] of a conclusion, evidence should be reliable and meet a rigorous [[burden of proof]]. Different professions have different standards for evaluating evidence as meeting, or falling short of, this burden.

== Medical and scientific evidence ==
'''Evidence''', as used in medicine and similar fields, refers to '''objective findings that help make predictions'''. This includes weighing the quality of the evidence itself.  

The quality of evidence depends on the methodology used. For most interventions in clinical medicine, the [[gold standard (science)|gold standard]] is the [[randomized controlled trial]], in which a treatment or lack of treatment can be applied to a sample of people who are randomly chosen to receive or not receive the treatment. For the highest-quality evidence, the sample must be similar to the population in question and must be big enough to have good {{wpl|statistical power||.}}

Some types of data are not amenable to randomized controlled trials, for instance, epidemiologic studies. Epidemiologists usually carry out [[case-control study|case-control studies]].

Another type of non-randomized study is the [[cohort study]], in which researchers observe groups of people for the existence of a disease. 

The lowest quality of clinical evidence comes from {{wpl|case report|case reports}} and from [[testimonial]]s, that is, from the anecdotal reporting of the experiences of an individual or of a small group of individuals. [[Statistic|Statistically]], these reports are meaningless [[anecdote]]s, but they can aid in identifying problems for study.

== The legal evaluation of expert scientific testimony ==
Anyone who frequents forums of Internet debate on subjects involving science will understand immediately the power of the "expert."  When invoked to support a proposition, whether properly used or not, the name of an expert lends the ring of credibility to even absurd subjects.<ref>See Ken DeMeyer's attempts to use [[Argument from authority|arguments from authority]] [[Essay:Social Effects of the Theory of Evolution|here]]. All those fancy titles sound impressive, until taken apart.</ref>    

Courts recognize this force: allowing "expert testimony" in court on matters of science, medicine, or other technical subjects has an extremely prejudicial effect and tends to persuade a naive jury more by authority than by actual reasoning. In short, junk science may hide behind fancy degrees. To avoid this prejudicial effect, courts have recently begun to hold ''gatekeeping hearings'' to prevent the introduction of junk science.<ref>''Daubert v. Merrell Dow Pharmaceuticals, Inc.'', 509 U.S. 579 (1993) (defining the court's gatekeeping function).</ref>  The court's gatekeeping duty, inferred from Federal Rule of Evidence 702, "imposes a special obligation upon a trial judge to 'ensure that any and all scientific testimony . . . is not only relevant but reliable.'"<ref>''Kumho Tire Co. v. Carmichael'', 526 U.S. 137, 147 (U.S. 1999) (citing ''Daubert'', 509 U.S. at 586).</ref>  If expert testimony is not reliable, it will run the risk of prejudicing the jury one way or another; thus, the expert testimony should not only be discredited and ignored by the jury, but it should not ''even be presented to the jury''.

''Daubert'' and its progeny lay out factors to consider when deciding whether or not evidence is reliable. Courts use a four-factor test, asking:
# Whether a theory or technique can be or has been tested,
# Whether the expert's testimony has passed through the processes of peer review and publication,
# Whether there is a high error rate in a theory or technique, and whether standards for evaluating such errors exist, and, most importantly,
# "Whether the theory or technique enjoys 'general acceptance' within a 'relevant scientific community.'"<ref>''Kumho'', 526 U.S. at 150 (citing ''Daubert'', 509 U.S. at 592-594).</ref>

Thus, expert testimony (scientific or otherwise) must pass a rigorous test to even be admitted at trial.  An expert's ''ipse dixit'' statements &mdash; i.e. "I am an expert, and I say this, therefore it must be true" &mdash; are not admissible of their own accord.<ref>''Kumho'', 526 U.S. at 157.</ref>  In short, experts should use in the courtroom the same degree of logical scrutiny demanded by their field.<ref>''Vargas v. Lee'', 317 F.3d 498, 500 (5th Cir. 2003).</ref>  Every step of the expert's analysis is subject to this exacting inquiry; no logical leaps are allowed, and the court should be able to follow an expert's reasoning from start to finish.<ref>''Knight v. Kirby Inland Marine'', 482 F.3d 347, 355 (5th Cir. 2007).</ref>  Further, where an expert draws support for a statement from a published study or other ''corpus'' of knowledge, the statement cannot run counter to the study: swearing one way based on a study that suggests the other is not allowed.<ref>''Doe v. Dallas Ind. Sch. Dist.'', 220 F.3d 380, 386 (5th Cir. 2000).</ref>

Zealous guardianship, therefore, characterizes the manner in which American courts treat scientific evidence.  The highest scientific standards are applied to any testimony by a so-called expert; no arguments from authority are allowed; and peer review, along with general scientific acceptance, is a ''must''.

==See also==
*[[Proof]]
*[[Scientific method]]
*{{wpl|Federal Rules of Evidence}}

==References==
{{reflist}}


[[category:law]]
[[category:science]]
[[category:Philosophy of science]]

Categories: law, science, Philosophy of science