Policing &
Reducing
Crime
FACE VALUE?
EVALUATING THE ACCURACY
OF EYEWITNESS INFORMATION
Briefing Note
Police Research Series Paper
Mark R. Kebbell & Graham F. Wagstaff
March 1999
Summary
Eyewitnesses play an important part in many crime
investigations. Hence it is important that the police
understand how to assess the reliability of the
information that witnesses provide. This paper provides
a practical summary of current research for operational
officers. Various factors have been identified that
influence the quality of eyewitness statements, in
particular:
•
•
•
the nature of the offence and the situation in which
it is observed;
the characteristics of the witness; and
the way in which witnesses are interviewed.
Research has found that, generally, witnesses are more
accurate with their descriptions of certain offender
characteristics (such as sex, hair colour and
distinguishing features) than others (such as age,
height and specific race). The ability of witnesses to
estimate correctly these characteristics will, however,
be partly determined by the physical characteristics of
the witnesses themselves. Hence, to evaluate the likely
accuracy of witnesses’ descriptions it is worthwhile
taking a description of the witness. The more similar the
descriptions are to one another, the more accurate the
offender description is likely to be.
Whilst the police have no control over the first two of
these, they can exert considerable influence on the way
in which information is retrieved through, for example,
interviewing techniques.
The characteristics of the witness
Factors relating to the crime
In general, children are poorer than adults in aspects of
the encoding, storage and retrieval of information and
this results in poorer memory. The ability of children to
give accurate accounts, however, depends on how they
are interviewed.
Many of the more critical factors which influence the
ability of eyewitnesses to give accurate information
were identified in the well known Turnbull Ruling (R. v
Turnbull and others, 1977). These broadly take account
of the conditions of the observation, the relationship of
the witness to the event and certain aspects of the
witnesses’ recollection of the event.
Whilst the Turnbull Ruling provides good general
guidance, it is important to be aware of exceptions. For
example, victims of serious crimes can sometimes
maintain accurate memories of an offence over a long
period of time as they tend repeatedly to go over the
event in their minds, thus aiding storage in memory.
Also, the presence of a weapon or threat of violence,
will increase the intensity of a witness’s experience, and
raise stress levels. Stress will lead to a narrowing of
witness focus and this is likely to concentrate attention
towards the incident itself and away from ‘peripheral
information’.
Research has identified a number of witness
characteristics that may also affect the accuracy of
eyewitness accounts.
The ability of older people to act as eyewitnesses is not
as good as that for younger or middle aged people. As
we age our perceptual abilities decrease, and from 40
years onwards this decline speeds up. Additionally,
older adults may have greater difficulties in storing and
retrieving information.
People with learning disabilities vary considerably in
their ability to report details, and are sensitive to the
ways in which questions are asked. They can, however,
often provide accurate accounts of events that they
have witnessed.
Although direct assessments of the influence of mental
illnesses such as depression and schizophrenia on
eyewitness memory are rare, research suggests that
A Publication of the Policing and Reducing Crime Unit
Home Office Research, Development and Statistics Directorate
50 Queen Anne’s Gate London SW1H 9AT
they can have an adverse effect.
Alcohol and drugs can have a negative effect on
memory performance. This effect is related to the
amount and type of the substance consumed.
Head injuries that result in unconsciousness, even
momentarily, usually lead to memory problems.
Although a victim who has been knocked unconscious
might not be able to recall critical information at first,
memory can return to them over time.
Interviewing eyewitnesses
The way in which witnesses are interviewed and their
responses interpreted has an important influence on the
quality of the information retrieved.
the accuracy of the information provided. Research in
controlled situations, however, shows that where there
has been no attempt to influence the witness, those who
claim to be ‘absolutely certain’ about something tend to
be correct.
Information from identifications
Witnesses can be good at recognising people and items
from an event even though they cannot accurately
describe or recall them. Research shows a reasonable,
but far from perfect, relationship between witness
confidence and identification accuracy when witnesses
actually make an identification at an identification
parade.
Recommendations
Research suggests that eyewitnesses are very good at
answering questions about ‘what happened’. Hence a
witnesses account of the actions of an offender can
often be accurate even if poor or inaccurate details are
given concerning the description of the offender.
Witnesses tend to provide the most accurate answers to
open questions. Even those groups with generally
poorer memories can show high accuracy rates for
open questions. As questions become more specific
and closed, so accuracy rates fall. Nevertheless,
‘closed’ questions (such as ‘what colour was his shirt?’)
may have to be used as a last resort to elicit information
about something a witness may have omitted to
describe in free recall.
The subtle use of language in questions can influence
witnesses by suggesting a particular response. The
phrasing of questions which suggest a particular
response, for instance leading questions such as ‘was
his shirt red?’’, can decrease accuracy levels even in
normal adults.
1.
It is important that investigators understand how to
assess the reliability of the information that
witnesses provide. Hence the contents of this
report need to be brought to the attention of police
trainers, crime investigators, crime analysts and
those responsible for interviewing witnesses and
victims.
2.
It is essential that those officers who interview
victims and witnesses are trained in the correct
interview techniques and that they employ these
skills during interviews.
3.
Since the ability of a witness accurately to describe
an offender will partly be determined by his or her
own physical characteristics, it will help routinely to
record these details.
4.
Much of the research into eyewitness accuracy has
been based on laboratory studies. Whilst their
findings are helpful for interpreting information from
an operational setting, they are a poor substitute for
the actual conditions which victims and witnesses
endure. Hence more empirical research is needed
based on actual cases. In particular, the factors
which influence the accuracy of facial composites
and the usefulness of these procedures to police
investigations should also be the subject of further
study.
5.
Eyewitness information is important. The police
should ensure that accurate records of offender
descriptions are kept, and that information systems
are designed to cope with the variability of
descriptions.
Particular issues need to be considered when
interviewing traumatised witnesses. Retrieval of
information in these circumstances can be improved
through remembering what was experienced
emotionally during an event in order to provide retrieval
cues.
Although it is usually assumed that witness
confidence is correlated with the accuracy of the
information that they provide, this is not always the
case. The style of questioning can influence the extent
to which a witness feels confident about information.
This can lead to an over-optimistic assumption about
Papers in the Police Research, Reducing Crime, Special Interest Series and other PRC ad hoc publications are available free of
charge from: Home Office, PRC Unit Publications, Room 455, 50 Queen Anne's Gate, London, SW1H 9AT.
Facsimile no. 0171 273 4001.