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.