Criminal courts have to deal with the use of scientific evidence all of the time. Numerous tests are employed. A breath test used to assert a DUI charge, a drug test designed to identify potential illegal drugs or a test that claims a hair follicle or tire tracks are connected to the accused.

In a disturbing circumstance of “That’s how it’s always been done,” experts were permitted to testify that marks on a gun casing match those of a gun in the possession of a suspect, based on little more than their own asserted expertise.

This is because there is very little genuine science underlying many of these tests or assertions. While a properly performed drug test should be able to identify the chemical composition of substance and determine it the white powdered is cocaine, there is much less scientific support for claims made regarding many other “scientific” tests, which often are little better than educated guesses.

For some tests, there are real problems in developing a statistically rigorous method of identifying items as common as fingerprints and ballistic markings. Some evidence may be unusable and inadmissible, such as bite marks, which one state commission on the use of evidence in criminal cases has found so problematic, that it has recommended that its use should be prohibited.

This may be the only solution to prevent this questionable material from unfairly influencing juries. Opinion evidence that masquerades as “scientific fact” can receive far more weight from a jury that it is entitled to, and jury instructions may not be adequate to counterbalance this improper valuation.

Evidence that is afforded the title scientific needs to comport with the minimum standards of science. Otherwise, it may be little more than one person’s opinion.

Source: sciencemag.org, “Reversing the legacy of junk science in the courtroom,” Kelly Servick, March 7, 2016