Figure 1:

Example of how Equation 1 is used to estimate the standard error of measurement when the amplitude of the P3b wave is scored from an averaged ERP waveform as the mean voltage across a measurement window of 350–550 ms. To compute this standard error, the mean amplitude score is obtained from the single-trial EEG epochs, and these single-trial scores are used to compute $SD/\sqrt{N}$. SD is the standard deviation of the single-trial mean amplitude scores, and N is the number of trials. The result is the standard error of measurement for the score obtained from the averaged ERP. Separate standard error values can be obtained for each experimental condition (e.g., rare trials versus frequent trials in an oddball paradigm). This approach is possible because the mean amplitude score obtained from the averaged ERP waveform is equal to the average of the single-trial mean amplitude scores. This approach does not work with other scoring methods, such as peak amplitude and peak latency. Note that only a subset of the single-trial epochs used to create the averaged ERP waveform are shown here.