Letter: Truth is, polygraph is not an exact science

Monday, May 7, 2007 | 7:15 a.m.

T he Las Vegas Sun's April 30 article on polygraph testing of sex offenders, "If the chair doesn't get them, the polygraph will," was an unwitting but pointed indictment of how the polygraph is misused and misrepresented by law enforcement.

Although polygraph results are considered to be too unreliable to be admissible in most U.S. courts, law enforcement often exaggerates the accuracy of the polygraph or even falsifies results to elicit confessions. Ironically, a column in the same issue of the Sun noted that in one-fourth of the cases involving a convicted person exonerated by DNA evidence, a false confession had been obtained. Statistics show that many false confessions by innocent people follow "failed" polygraph tests.

Parole officer Debbie Lupe is quoted in the article as saying, "If you haven't done anything wrong, you have nothing to worry about." Yet research shows that the polygraph is more likely to err with innocent people than with guilty ones.

Other studies have found that the conclusions made by polygraph examiners are very much influenced by the examiner's biases, not surprising given that the typical examiner receives less training than many massage therapists.

Lupe's comments that well-behaved offenders make her "nervous," and when a test is inconclusive she will "keep testing until she gets something" are hardly indicators of an unbiased, neutral attitude.

Should true sex offenders be held accountable for their actions? Of course. Should people be punished based on questionable science alone? No, and that's the real truth.

Mark J. Chambers, Henderson

The writer is a forensic psychologist who has testified in court as an expert witness on the issue of polygraphs.