Poor impulse control is a common feature in patients with Parkinson's disease (PD). However, before testing whether patients with PD and controls differ in impulsivity, one must assess whether impulsivity measures are invariant across groups. Consequently, we examined (a) the measurement and structural invariance of a scale assessing changes in four dimensions of impulsivity (urgency, lack of premeditation, lack of perseverance and sensation seeking) among patients with PD and controls; and (b) whether the four impulsivity traits relate differentially to risky decisions by patients.

Close relatives of 78 patients with idiopathic PD and 96 control participants were given the short Urgency–Premeditation–Perseverance–Sensation seeking Impulsive Behaviour Scale (UPPS), which assesses changes in four dimensions of impulsivity. Participants also completed the Game of Dice Task (GDT), a laboratory measure of risk taking.

Multigroup confirmatory factor analyses supported measurement invariance across groups, whereas structural invariance was not confirmed. Patients with PD showed greater variability and higher impulsivity than controls. Furthermore, patients with impulse control disorders (ICDs) demonstrated even greater levels of sensation seeking than patients without ICDs. Finally, lower premeditation and greater perseverance were significantly associated with greater risk taking in patients with PD, and higher agonist dopaminergic doses with less risky choices on the GDT.

The questionnaire appears to function comparably across patients and controls. Thus, group comparisons on the questionnaire can be considered valid. Mean differences between groups on the dimensions of impulsivity may reflect executive impairments and/or abnormal reward processing in patients with PD, which may lead to risky behaviours.