JUNEAU — The Alaska Supreme Court has ruled that a common polygraph test fails scientific tests for reliability and is unsuitable for use as evidence.

The ruling, which addressed three cases brought to the court, was issued Friday.

Polygraphs have generally been forbidden as evidence in Alaska criminal trials since a 1970 Alaska Supreme Court case, but that decision and subsequent cases focused on prosecutors' ability to use polygraph results as evidence, said John Skidmore, head of the criminal division for the Alaska Department of Law.

In those cases addressed by Friday’s ruling, defense attorneys sought to use a type of polygraph test called the “control question test” to bolster their defense.

“Our opinion here does not mean that CQT polygraph testing will never be sufficiently reliable to pass muster as scientific evidence, but absent substantial evidence demonstrating that CQT polygraph testing produces reliable results based on sound, verifiable science, the results of CQT polygraph examinations cannot be admitted in evidence over objection," the justices wrote.

Other uses of polygraphs, such as for security screening, were not addressed.

Quinlan Steiner is head of the Public Defender Agency, whose attorneys represented some of the defendants behind Friday’s ruling. He said polygraph testing offered a way for defense attorneys to prove a confession is false or coerced.

“This (test) would’ve been a potential way to counter confessions as evidence in a court case. That is foreclosed by this opinion,” he said.

In the control question test, an examiner connects a variety of sensors to the body of the person who is to be tested. Those sensors measure heart rate, blood pressure, skin conductivity and other physical characteristics that are not typically regulated consciously. According to a description of the test published by the American Psychological Association, the person being tested is then asked a variety of questions. For some of the questions, the answers are known and agreed upon: “What is your mother’s name?”

For others, the answers are not: “Did you kill her?”

Proponents of the control question test say that by measuring the subconscious physical responses to a lie, the test discerns truth from fiction.

“The cumulative research evidence suggests that CQTs detect deception better than chance, but with significant error rates, both of misclassifying innocent subjects (false positives) and failing to detect guilty individuals (false negatives),” the Psychological Association’s description states.

In the three cases that led to Friday’s decision, defense attorneys attempted to use negative polygraph test results as evidence that their clients did not commit specific crimes.

Trial judges split: Two judges allowed test results to be admitted into evidence, but one did not.

With lower courts divided, the issue went to the Alaska Supreme Court. Justices there did not agree with the basic assumption behind the control question test, that a liar will have a different physical reaction from someone telling the truth.