Double-Blind Procedure

A fourth factor concerns whether a double-blind pro- cedure is used. There always exists the risk that a police officer who administers a lineup—typically containing a suspect and some innocent foils—will inadvertently steer a witness’s identification decision, most likely to the sus- pect (who may or may not be the culprit). For that reason,

social psychologists have argued for a procedure in which not only the witness is “blind” as to who the suspect is but so is the officer who administers the lineup.

In a study that specifically addressed this question, Sarah Greathouse and Margaret Bull Kovera (2009) paired student “witnesses” to a staged theft with student “police” who were trained how to administer a simultaneous or sequen- tial photo lineup using either biased or unbiased instructions. In these lineups, a picture of the actual culprit was either present or absent. Half the administrators were informed of who the police suspect was in the lineup; the other half was blind as to the suspect’s identity.

The results showed that under relatively biasing conditions (simultaneous photo spreads and biased instructions), witnesses made more suspect identifications— even when the suspect was truly innocent—when the administrator was informed rather than blind. Videotapes of the sessions showed that the informed administra- tors unwittingly increased identification rates by telling witnesses to look carefully, by asking them to look again when they failed to make a selection, and in some cases by letting on that they knew who the suspect was. This research strongly sup- ports a point of reform, recently adopted in several states, that eyewitness research- ers have long advocated: a double-blind procedure in which neither the suspect nor the police administrator know who the suspect is within the lineup.