The reasons for not recording the “post test interview” are essentially the same as those that hold for not recording mistreatments that precede any confession obtained by duress, with the exception of one reason that is specific to the polygraph in an age where video recording is readily available.

That reason lies in the fact that once a judge or a jury has seen the sort of thing that actually goes on in this so-called “test”, they abandon the idea that this is a test in the sense that an IQ test is a test.  When watching such a video, I usually ask them whether they would consider an IQ tester behaving appropriately if, after administering the test to the testee, the tester would then begin to badger the testee about having failed the test, thereby showing himself to be a stupid ignorant bastard (psychological rubber hose) or, perhaps, someone who needs a lot of emotional help that the tester is, fortunately, able to provide (the sympathetic, “big brother/priest” version, where, in the case of the polygraph, confession is said to be good for the soul).  If you go to item #29 on http://www.psych.utoronto.ca/~furedy/polygraph.htm, there is a long video that includes a case shown 60 minutes of a woman accused of murder being “tested” in this way by a couple of “testers”.  The Texas police were silly enough to make this video as a “training” film for their would-be polgraphers, but since then polygraphers have wised up, and are bit more cautious.  Still, even written transcripts or even notes made by the polygrapher can be useful for establishing that the polygraph is not a standardized psychological test, but a dynamic, undstandardizable interrogatory interview whose main purpose is not to detect deception (or even guilt), but to extort a confession.

All the best, John