One of the most basic principles of science is the objectivity of the scientist conducting a given experiment. One of the most critical tools for ensuring that objectivity, particularly in the social sciences where humans and other animals are the subjects of the hypothesis being tested, is the “double-blind” procedure — which is to say, neither the administrator of the procedure nor its subjects should know the desired outcome in advance, as a means of protecting against intentional or unintentional cues leading subjects to reach one conclusion over another for reasons other than the effects of those variables expressly being tested. And it is well-established that good intentions on the part of the scientist are insufficient to prevent the influence of her bias.
The relevance? A police lineup is a scientific experiment: It is a test of a witness’s ability to recall the identity of the perpetrator from her independent memory of the events at issue. When the administrator of the lineup knows the desired outcome of the experiment, i.e. the selection of the police suspect, the witness is reduced to a horse that can’t really count, but is really good at following instructions. It is known among scientists that objectivity cannot be left to the humans conducting a given experiment. Instead, experiments must be controlled in a manner that preempts the possibility of subjective bias, and otherwise the integrity of the discipline is compromised and all results are suspect.
Police are no better at controlling unintentional cues that betray their knowledge of the identity of their suspect, than scientists are at controlling their desire for a hypothesis to be borne out empirically. However strong the commitment to truth-seeking, both share the hope that their suspicion will prove true. This is why it is crucial to the integrity of the justice system that police lineup administrators either not know the identity of the suspect or his position in the lineup, or that a procedural mechanism is put in place to create the same effect (for example, like they do in Wisconsin (PDF) — and Hennepin County, Minnesota, and Northampton, Massachusetts).
But police and the courts continue to resist the insights of science. Just last week, a California appellate court in People v. Cisneros (2007 WL 901728 (Cal.App. 2 Dist., Mar 27, 2007)), in response to the defendant’s claim that the non-blindness of the lineup administrator added to its suggestivity, came out boldly against the scientific method and held that “the identity of the person who prepared the lineup is not relevant to a determination whether the lineup was unduly suggestive.”
One hundred years after Hugo Munsterberg made his pitch that the court open its doors to the sciences, statements like the above make it clear that the doors remain largely shut.