Cognitive Estimation in Non-demented Parkinson's Disease

Objective: The Cognitive Estimation Test (CET) is widely used in clinical and research settings to assess the ability to produce reasonable estimates to items that individuals would not know that the exact answer (e.g., "How fast do race horses run?"). We examined the performance of non-demented Parkinson's disease (PD) patients on the CET, because previous studies reported heterogeneous results about possible cognitive estimation impairments in PD. We also examined whether PD patients improve their performance if given the chance to reconsider their initial CET responses. Methods: Thirty non-demented idiopathic PD patients and 30 healthy controls matched in age, gender and years of education performed the two parallel forms of Italian CET. The estimation scores for initial and final responses as well as the number of times individuals changed their answers were examined. Additional neuropsychological tests, evaluating intellectual, frontal executive, speed of processing, naming and arithmetical abilities, were also administered. Results: The PD group were not significantly poorer than healthy controls at estimating the answers to items on either CET versions. Moreover, PD patients did not significantly differ in their initial and final responses or number of response changes. Performance on the CET was significantly related to performance on a global measure of executive function, processing speed and arithmetic. However, PD patients were impaired compared to controls on the component involving mainly, but not exclusively, length-related estimations. Conclusions: Non-demented PD patients have mild impairments in cognitive estimation ability, which may depend on the estimations they are required to provide.