TABLE 2.

VEP Correlations with Age or CSS

	Correlation with Age				Correlation with CSS RTT, n = 34
	TD, n = 20		RTT, n = 34
Measurement	r	P	r	P	r	P
N1 latency	−0.23	0.326	0.32	0.069	−0.26	0.136
P1 latency	0.02	0.935	0.20	0.263	−0.37	0.031
N2 latency	0.16	0.513	−0.02	0.933	−0.04	0.845
P1–N2 time	0.17	0.484	−0.05	0.776	−0.04	0.808
N1 amplitude	0.22	0.349	0.36	0.036	0.19	0.276
N1–P1 amplitude	0.16	0.508	−0.32	0.070	−0.18	0.313
P1–N2 amplitude	0.20	0.394	−0.31	0.079	−0.07	0.712

Latency values are in milliseconds, and amplitude values are in microvolts. r indicates Spearman correlation coefficient. Significance threshold was set to p < 0.007 after correction for multiple comparisons.

CSS = Clinical Severity Score; RTT = Rett syndrome; TD = typically developing; VEP = visual evoked potential.