Faking handedness: Individual differences in ability to fake handedness, social cognitions of the handedness of others, and a forensic application using Bayes’ theorem

Abstract

ABSTRACT People usually describe their handedness honestly, but that need not necessarily be the case. A legal case is described of a murder said by the pathologist to be committed by a left-hander but the defendant claimed to be right-handed, and the first author assessed the defendant’s handedness as an expert witness. We know of no previous work on faking handedness, and so we tested 30 right-handers and 25 left-handers on various handedness tasks, and then asked the participants to repeat the tasks while faking being of opposite handedness. Social cognitions of handedness were assessed from participants’ knowledge of how other right- and left-handers would answer handedness questionnaires. Fake handedness was best differentiated using cursive lower-case sentence writing, upper-case written letters being less good at distinguishing, as also were simple motor tasks. Participants differed in social cognitions of handedness, and those with more accurate social cognitions were better able to fake. Personality measures did not predict faking ability. For forensic purposes a Bayesian analysis was carried out to evaluate the likelihood of right and left hand performance being true rather than faked, and the cursive lower-case writing provided strong posterior odds that, as claimed, the particular defendant was a true right-hander.