So, how should the photographs used in the
line-up be presented to the eyewitness?
One choice is whether we present the photographs
simultaneously – that is, they are laid
out side-by-side in front of the eyewitness
so they that could all be viewed at once.
However, one problem with this approach is
that it may encourage relative rather than
absolute judgements.
That is, eyewitnesses approach the task as
being to determine who in the line-up looks
relatively most like the criminal – rather
than an absolute decision as to whether the
criminal is actually present or not.
That is, the structure of simultaneous line-ups
may foster the same sort of bias to pick someone
as biased instructions do.
What can we do about this?
Well, one alternative is to use a strategy suggested
by Roderick Lindsay of Queen’s University
and Gary Wells of the University of Alberta,
known as the sequential line-up.
This is where each member of a line-up is
viewed in turn.
The eyewitness is asked, “Is this the person
you saw?”. And they have to answer “yes”
or “no”.
In the ideal version of this, eyewitnesses
wouldn’t know in advance how many photos
will be in the line-up, and the procedure
will stop on the first positive ID.
The idea is that - with a sequential approach
- we minimise that implicit imperative for
eyewitnesses to compare the line-up members
with one another – that problematic relative
judgement.
Instead they are effectively being told to
compare each individual against their memory
of the real criminal.
That is, they’re making an absolute judgement.
And it’s the absolute judgement that we
want.
That’s the principle.
But is there any evidence to suggest that
using the sequential rather than the simultaneous
presentation helps witnesses correctly identify
the suspect more often?
Nancy Steblay of Augsburg College and her
colleagues did a meta-analysis of thirty research
studies looking at this very question – and
concluded that using the sequential line-up
procedure did indeed result in fewer false
identifications than simultaneous presentations.
There was some evidence that sequential line-ups
resulted in fewer correct hits as well as
fewer false positives – following the same
reasoning with biased instructions.
However, in this case, Nancy Steblay reported
that when she took more realistic conditions
into account – this effect largely disappeared.
That is, sequential line-ups didn’t result
in fewer correct hits when real world factors
were considered.
So, the current consensus appears to be
that sequential line-ups are better practice
than simultaneous line-ups.
One other technique that’s been investigated
by psychologists, to address the issue of
response bias in eyewitnesses, is to first
deliberately show them a blank line-up, where none of the members of the line-up are the
suspect.
The idea is that if your eyewitness does
pick someone from the line-up that you know for sure has no criminals in, then this may
indicate that their judgement on the real
line-up should be called into question.
You’ve essentially screened them for an
inappropriate response bias.
Gary Wells investigated whether this strategy
worked or not, and he found that whether
or not eyewitnesses made a false ID on the
blank line-up predicted whether they would
make a false ID on the real line-up.
That is, we have evidence that this technique
works.
In our next presentation we’ll turn our
attention to the members of the line-up who
aren’t the suspect – the people we know
are innocent and how we ought to go about
choosing them.
