This paper addresses some practical issues related to the calculation, display and assessment of the significance of changes in the average time–frequency energy density of event-related brain activity. Using scalp EEG and subdural ECoG example datasets, parametric tests are evaluated as a replacement for previously applied computer-intensive resampling methods. The performance of different estimates of energy density, based on matching pursuit, scalogram and spectrogram, and their Box–Cox transformations is evaluated with respect to the assumption of normality required for the t-test, and the consistency of the final results.