I'm a co-founder of AntiPolygraph.org, a website dedicated to exposing and ending polygraph waste, fraud, and abuse. ABC News did a poor job explaining polygraphy in its Polygraph Q&A. Perhaps your biggest mistake was basing your article solely on what you were told by people who depend on polygraph testing for a living.

For example, you quote polygrapher Frank Horvath as saying that polygraph critics say polygraphy is 70% accurate. But in reality, polygraph critics are more likely to argue that polygraph "testing" has no scientific basis at all! See, for example, Professor William G. Iacono's recent article, "Forensic 'Lie Detection': Procedures Without Scientific Basis":
 
http://antipolygraph.org/articles/article-018.shtml 
 
Regrettably, your Polygraph Q&A completely failed to explain how truth vs. deception is actually inferred during a polygraph interrogation. No doubt, the polygraphers you interviewed didn't tell you. The dirty little secret of the polygraph trade is that the "test" actually depends on trickery: the polygrapher must lie to and other otherwise deceive the person being "tested" about the nature of the procedure.

The key deception is that the polygrapher, while admonishing the examinee to answer all questions truthfully, secretly assumes that denials in response to certain questions -- called "control" questions -- will be less than truthful.

One commonly used control question is, "Did you ever intentionally hurt someone?" The polygrapher deliberately steers the examinee into a denial by suggesting, for example, that the kind of person who would intentionally hurt someone is the kind of person who would commit the crime under investigation.

The polygrapher scores the test by comparing physiological reactions to these probable-lie control questions with reactions to relevant questions such as, "Did you cause your daughter's death?" If the former reactions are greater, the examinee passes; if the latter are greater, he fails. This simplistic methodology has no grounding in the scientific method.

Investigators value the polygraph because naive and gullible examinees sometimes make damaging admissions. But many truthful persons are falsely accused in the process. Perversely, the test is biased against the truthful because the more honestly one answers the control questions, and as a consequence feels less stress when answering them, the more likely one is to fail.

Conversely, liars who understand the trickery behind the test can easily beat it by covertly augmenting their physiological reactions to the control questions. This can be done by constricting the anal sphincter muscle, biting the side of the tongue, or merely thinking exciting thoughts. These techniques are explained in detail in AntiPolygraph.org's free book, The Lie Behind the Lie Detector, which may be downloaded as a PDF file at:
 
http://antipolygraph.org/pubs.shtml 
 
No reliance whatsoever should be placed on the outcome of pseudoscientific polygraph "tests."