Secrecy News

David Lykken and the Polygraph Myth

David T. Lykken, a psychologist who did pioneering research and public education on the limits and abuses of polygraph testing, died last week at age 78.

With exceptional clarity he demonstrated that the polygraph is not a “lie detector” but simply a recorder of physiological responses to verbal stimuli. And, he explained, there is no set of physiological responses that corresponds uniquely to deception.

That does not mean the polygraph is worthless. There is empirical evidence to support its use in the investigation of specific incidents, where “guilty knowledge” of particular details may be usefully revealed by the polygraph.

“The use of the [polygraph] by the police as an investigative tool, while subject to abuse like any other tool, is not inherently objectionable,” Lykken wrote.

(Not only that, “It seems reasonable to conclude that whether O.J. Simpson did or did not kill his wife could have been determined with high confidence using a Guilty Knowledge Test administered within hours after he was first in police custody.”)

On the other hand, he said, the use of the polygraph for security screening of personnel, as is commonly done by U.S. intelligence agencies, cannot reliably achieve its purported goal of identifying spies or traitors and in many cases becomes counterproductive.

“I think it is now obvious that polygraph testing has failed to screen out from our intelligence agencies potential traitors and moles. On the contrary, it seems to have served as a shield for such people who, having passed the polygraph, become immune to commonsense suspicions.”

Lykken produced a body of work that is prominently cited in every bibliography of polygraph-related research. And he addressed the interested public in a highly readable 1998 book called “A Tremor in the Blood” (an allusion to Defoe), which is full of colorful observations as well as analytical rigor.

So, for example, he reports that Pope Pius XII condemned polygraph testing in 1958 because it “intrude[s] into man’s interior domain” (Tremor, page 47).

And “when Bedouin tribesmen of the Negev desert were examined on the polygraph, they were found to be far less reactive than Israeli Jews, whether or Near Eastern or European origin” (page 273).

Dr. Lykken was profiled in a September 20 obituary in the New York Times.

It is a sign of our times that the scientific critique of polygraph testing has gained almost no traction on government policy. To the contrary, the use of the polygraph to perform the sort of screening that Lykken termed a “menace in American life” is actually on the rise.

“From FY 2002 through 2005, the FBI, DEA, and ATF conducted approximately 28,000 pre-employment polygraph examinations” as well as tens of thousands more for other purposes, according to a major new report from the Justice Department Inspector General.

See “Use of Polygraph Examinations in the Department of Justice” (pdf), September 2006.

Characteristically, the new Inspector General report did not even consider the question of the polygraph’s scientific reliability.

In particular, as George Maschke of AntiPolygraph.org told CQ Homeland Security, the Justice Department report failed to grapple with a 2002 finding of the National Academy of Sciences that “[polygraph testing's] accuracy in distinguishing actual or potential security violators from innocent test takers is insufficient to justify reliance on its use in employee security screening in federal agencies.”

Aldrich H. Ames, the former CIA officer whose years of espionage against the United States went undetected by the polygraph, reflected on the mythology of the polygraph in a letter that he wrote to me from federal prison in November 2000.