What makes scientific evidence scientific?

Close examination of many types of so-called scientific evidence has found that much of it is little more than opinion and educated guesses

In a criminal trial, some types of evidence are more compelling. A witness stating they saw a person in a dark alley is one thing, but a clear video of a person on a surveillance camera is much stronger evidence and more convincing to a judge or jury.

The reason breathalyzers are used by the California Highway Patrol and local law enforcement for DUI stops is because the average juror is going to view a 0.15 blood alcohol content measurement as much more powerful than merely having a trooper testify that the accused failed the more subjective field sobriety tests.

A device that seems objective and one that makes a cold, hard "scientific" assessment appears to be much more reliable than a fallible human, who could feel pressured to make an arrest to meet a quota or who may be overly zealous in stopping anyone they suspect of driving while intoxicated.

But is it really science?

The problem is, even many types of so-called scientific evidence, upon closer examination, may prove to be much less authoritative than they have long been held to be. It has been called "junk science," and much of it is used every day in courts in California and across the nation.

There have been a few especially egregious cases in Texas, which resulted in the state setting up of a special commission to examine the types of evidence admitted in their courts. Questions have been raised with regard to "so-called pattern evidence, such as fingerprints, shoeprints, tire tracks and bite marks."

The commission has recommended that bite mark evidence is so prone to error and inaccuracy that its use be stopped. However, virtually any evidence that is "identified" by pattern recognition, including items like ballistic markings on bullets and shell casing and arson investigations, which often rely on burn patterns on walls and ceilings, are equally subject to error. One man in Texas may have been executed because of a now widely discredited arson analysis.

Researchers looking at something as well-accepted as fingerprint analysis found that developing a scientifically rigorous method of matching the patterns was far more difficult that might be expected for evidence that is routinely used in court.

What is scientific evidence?

This type of evidence needs to be examined closely because is given extra authority because it carries the veneer of "Science." A jury needs to know that a fingerprint and hair follicle analysis is more like an opinion of someone who has been trained to observe these items, and less like the measurement of a thermometer. An expert's opinion is just that; it is an "opinion" and it may be subject to a significant degree of error and variation.

The high degree of error in much of this testimony has been found virtually everywhere it has been examined. Even the FBI used testimony that was later discovered to have errors in 90 percent of the cases reviewed involving hair follicle testimony.

Wrongful convictions due to shoddy forensic evidence and testimony matter. Not only is an innocent individual sent to jail for a crime they did not commit and the prosecution is a waste of the resources of the state, but it also means a guilty party has escaped prosecution and remains free.