Eyewitness Identification: Field Studies

A substantial base of laboratory research is now available to aid our understanding of eyewitness identification processes and to support recommendations for lineup reform. However, there are also a limited number of peer-reviewed, published studies that measure eyewitness responses in real police cases. Although few, the studies include large-scale investigations involving a sizable combined sample of eyewitnesses (4000+). The traditional simultaneous lineup format in these studies produces a modal suspect identification (SI) rate of around 40% to 50% and a filler selection rate of approximately 20%.

Field studies bring unique strengths and weaknesses to research efforts, capturing eyewitness decisions in the most forensically relevant settings but under circumstances that lack the control and precision of the lab. Existing field studies—archival summaries of police reports and descriptive data from pilot research—effectively augment laboratory findings.

Each witness decision for a field lineup falls into one of three response categories: (1) an SI, (2) a filler identification, or (3) no choice from the lineup. A challenge for eyewitness field research is that an unknown percentage of real-world lineups do not include the perpetrator. Suspect selections cannot be directly equated with accurate identifications, because any false identification of an innocent suspect is contained within the SI category. Filler selections (foils [innocent persons] or false alarms) are known errors and signal investigators that the witness has a poor memory or is uncooperative, or that the filler is a better match to the offender than is the suspect. “No choice” responses (a lineup rejection) include witnesses unable or unwilling to make a lineup selection. These limitations of data interpretation must be kept in mind as the following field studies are examined.

Archival field studies provide baseline data regarding eyewitness responses under traditional lineup practice—a simultaneous display of lineup members administered by an investigator who knows the identity of the suspect. Some field information is also available for showups—a single-member lineup.

An early examination of 224 identifications made by eyewitnesses to real crimes in California revealed an SI rate of 56% and a showup SI rate of 22%. A year later, a 1994 study in Vancouver, Canada, detailed 170 identification attempts, 90% from simultaneous photo lineups. The authors reported SI rates for robbery victims (46%) and witnesses (33%) and for fraud victims (25%).

[Page 291]A larger sample of police files was reviewed in 2001 for 689 California identification attempts following crimes ranging from homicide to theft. Similar rates of SI were found for 284 simultaneous photo lineups (48% SI) and 58 live simultaneous lineups (50% SI). Live lineup decisions produced 24% false alarms and 26% lineup rejections. (Researchers do not always separate filler and “no choice” decisions, often because police reports do not provide this level of detail.) Showup identification rates were similar whether live (258) or photo (18)—76% and 83% SI, respectively—and significantly higher than rates for the full array. Of particular interest were 66 lineup identifications by eyewitnesses who had made an earlier identification of the same suspect. Significantly more SIs were made in later attempts (62%) compared with witnesses attempting a single identification (45%). A 2005 update of the California simultaneous lineup data, including overlap with the earlier data set, produced an SI rate of 52% for photo and 46% for live lineups; filler picks were at 15% for the overall group.

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