(b) Discuss the problems of conducting research into the detection of lies. (15)
For convenience, the sample often used in lie detection research has largely consisted
of a rather biased student population (i.e. laypersons). Participants are asked to tell
lies to see if they can avoid detection. Whilst the study by Mann et al is much more
meaningful in using a relatively large sample of police officers, there is no comparison
with laypersons. The sample is also ethnocentric: officers are all British and selected
from one particular constabulary, Kent. Police officers from other constabularies /
countries may be trained differently and so rely on different cues in detecting lies. It
would also be useful if research in this field were conducted on so-called professional
lie-catchers – i.e. members of the secret service, immigration officers etc – to see if
they perform even better than ordinary police officers.
Experimental research in this area has suffered from a lack of ecological validity
since it has largely been based on students telling low-stakes lies (sometimes with an
added financial incentive). However, the research by Mann et al is much more valid
since it featured high-stakes lies told by real suspects in police interviews (although in
reality, officers would normally conduct rather than just watch such interviews).
There are also ethical limitations to lie detection research in forensic psychology.
Low-stakes lies reduce the possibility of distress and embarrassment for the
participant, as does excluding laypersons from watching highly sensitive material
whereby the identity of suspects is revealed.
Experimental work in lie detection tends to gather exclusively quantitative data,
where % of the time that participants correctly identify a lie / the truth often
representing the dependent variable. Such work tends to suffer from methodological
reductionism since participants have a 50/50 chance of giving a correct answer. The
Mann et al study, however, successfully addressed this possible limitation by asking
officers an open-ended question about the cues they had used to detect deceit,
thereby gathering much useful qualitative data. It is unclear though as to exactly why
ordinary police officers perform better than chance level.
Finally, the kind of research / equipment that the researcher uses to measure lying
depends largely on their psychological approach. A physiological psychologist would
focus on possibly more scientific and objective instruments of lie detection such as
polygraphs, whereas a social psychologist would focus on those more subjective non-
verbal cues present (or not) in suspects’ behaviour. Either approach may be subject to
mis-interpretation.