The Misinformation Effect in the Interviewing of Witnesses

The misinformation effect is memory impairment after exposure to misleading information. It occurs when misleading data is received after the memory was originally made, causing memories to be altered. This is not a deliberate attempt to falsify memory. Instead, witnesses still think that they are remembering accurately, because their memories have changed to match the new information without the witnesses’ conscious knowledge.

Inaccuracy of eyewitness testimony

Most people believe that, in cases where the witness has no reason to be biased, the only valid reason to question witness testimony is the visibility conditions at the time of the crime. Thus, if eyewitness testimony is not discredited during the original court case, it often becomes the clinching evidence to cement a conviction.

However, several other factors can cause eyewitnesses to wrongly identify a person, including the misinformation effect. Eyewitness accuracy falls sharply within 20 minutes of the original event. At the same time, eyewitness memory is constantly vulnerable to contamination as a result of information received after the event.

In fact, although eyewitness evidence is usually given the most weight in court, it may be among the least accurate form of evidence. Among convictions later overturned by DNA evidence, more than 90% of convictions were based on eyewitness evidence.

Police lineups and the misinformation effect

The way in which lineups and other police and courtroom procedures are conducted can cause a witness’ memories of an event to be altered. When the eyewitness is presented with lineups in which the criminal is not present, the eyewitness is likely to misidentify a member of the lineup as the perpetrator. In some cases, merely being presented with a police suspect can be enough to cause misidentification.

This happens because when a witness is presented with a lineup or police suspect, the witness is led to believe that the person he saw is probably among those in front of him. The misinformation effect is strong enough to cause the witness to change his memories unconsciously to fit the assumed data of the suspect’s presence in the lineup. In this case, the misinformation effect can be countered by specifically instructing the witness that the perpetrator may not be present in the lineup.

Cross-examination and the misinformation effect

Although eyewitness accuracy continues to fall until 2 days after the event, the preparation of a witness to testify in court causes the witness to become more certain of his memory. However, the accuracy of the memory doesn’t change. An eyewitness who is prepared for cross-examination doesn’t have a more reliable memory of the perpetrator, but he thinks he does.

Even learning that another witness has identified the suspect increases the certainty of an eyewitness in the reliability of his memory. The increase in certainty is actually higher in cases where it later turns out the eyewitness was wrong. In one case where the suspect was later exonerated through DNA evidence, 5 separate witnesses had wrongly identified the suspect.

How to minimize the misinformation effect among witnesses

There is no absolute answer to the misinformation effect. It can only be minimized by establishing and following procedures which are designed to reduce the amount of implied information which could contaminate memories.

To reduce the number of misidentifications resulting in false convictions, the Department of Justice has published a set of best practices for conducting police lineups. One recommendation is to use known innocent fillers who closely match the victim’s description of the subject, especially when they have similarly unusual hairstyles or other distinguishing features.