A quantitative method for the assessment of overall effects from a number of similar electrophysiological studies: description and application to event-related potentials in Parkinson's disease.
Eight comparisons of auditory event-related potentials in idiopathic parkinsonism with matched controls were analysed using meta-analytic methods. Overall, there was clear evidence that P2, N2, and P3 peak latencies are delayed in patients. Effect sizes for the difference between patient and control latencies of N2, and to a lesser extent P3, were greater in studies with more cognitively impaired patients. High frequency high pass filter settings were significantly associated with shorter mean P3 latencies in controls, but not patients, so that greater effect sizes tended to be associated with higher high pass cut-off frequencies. These results support the argument for using quantitative methods for the review of clinical psychophysiological studies.