EvidenceProf Blog

Editor: Colin Miller
Univ. of South Carolina School of Law

Thursday, November 1, 2012

No Pregnant Pause: Illinois Court Rejects Defendant's Attempt To Analogize Home Pregnancy Tests To Polygraph Tests

As I noted in my post on Tuesday, in most jurisdictions, polygraph evidence is per se inadmissible. The conventional wisdom is that polygraph results are a lot less reliable than people, including jurors, think them to be. So, does the same logic apply to home pregnancy tests? That was what the defendant claimed in People v. Prather, 2012 WL 5295801 (Ill.App. 2 Dist. 2012). So, how did the court rule?

In Prather, Clarence Prather was charged wuth two counts of aggravated battery (victim pregnant), one count of obstructing justice, and two counts of domestic battery.  Prior to trial, the State filed a motion in limine seeking permission for the alleged victim (B.R.) to testify that she had used a home pregnancy test kit and had shown the positive result to the defendant.

Among other arguments, "Prather compare[d] home pregnancy tests to polygraph ("lie detector") tests, the results of which may not be used as evidence." The Appellate Court of Illinois, Second District, disagreed, concluding that

The supreme court has explained that polygraph tests pose a special danger because they suggest to jurors that they need not make their own credibility determinations (because the polygraph will tell them who is lying), but the tests are not sufficiently accurate and reliable to prove guilt or innocence....By contrast, home pregnancy tests do not purport to "testify" about the credibility of defendants or others, and thus do not encourage the jurors to abdicate making their own credibility assessments. Although the defendant argues that home pregnancy tests might have a tendency to over-persuade a jury in excess of their actual reliability, they are no different from other forms of scientific evidence or test results in that regard, and their reliability may be challenged at trial in the same manner. Accordingly, there is no basis for extending the per se bar against polygraph evidence to home pregnancy tests.



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The appeals court has argued itself into a circular box and I agree with the trial judge. The underlying problem is that the defendant could have only been given fair notice of the pregnancy if the test was actually correct. So there is no way to avoid the underlying question of whether not the test was valid and conducted properly. And it seems to me that a home test /of any kind/ presents unique challenges because the test is by definition not conducted under controlled conditions by trained personnel. So in that regard home tests are indeed very much different from other scientific evidence in their ability to over-persuade a jury.

The problem for the state is that it has two argue two things. It has to show that she was indeed pregnant and that the defendant knew it. It wants to use two different tests to achieve that end; one test to show she was actually pregnant and another, different, test to show that the defendant had reason to believe she was pregnant but not for the purposes of demonstrating she in fact actually pregnant. No.

There is a really good lesson here about the difference between what psychologists call episodic and semantic memory. I'd argue that for the mens rea of a crime to exist it has to be a semantic fact, not an episodic fact. The only way for the defendant to have formed a semantic memory of the fact is for the underlying home test to be true. So whether it was introduced to prove the fact of the pregnancy or the fact of the defendant's knowledge of the pregnancy both cases require the assumption that the test was validly conducted by a scientifically accepted instrument, neither of which has been demonstrated to true in this case.

Posted by: Daniel | Nov 1, 2012 2:00:05 PM

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