Note that the mean P1 peak amplitude variability, measured as the MAD estimate of the P1 peak amplitude from the raw EEG data in the TD group, was 0.37. This broadly concurs with existing data in which the coefficient of variation of VEP amplitude recorded in 100 healthy adults from electrodes positioned above the occipital cortex was reported to be 0.41 (Klistorner and Graham, 2001). However, given that the MAD estimator is less influenced by outlying data points than the coefficient of variation, estimates of variability from this statistic tend to be lower than from the coefficient of variation, so a direct comparison between these two statistics cannot be made. For comparison, the co-efficient of variation of P1 amplitude in the TD group, based on the SD of these data was 0.58, i.e., higher than that reported by Klistorner and Graham (2001) – possibly reflecting developmental change in amplitude variability.
