Table 2.

Summary of non-parametric statistics performed by the Mann-Whitney rank sum test on PERG amplitude and latency in MSA, early IPD patients and control subjects (C). The reduction in amplitude in PD patients was highly significant for all stimulus conditions, whereas the latency increase was highly significant for the B-Y stimulus only

Group	Median	25%	75%	Mann-Whitney (patients versus controls)	Mann-Whitney (MSA versus IPD patients)
	Amplitude
MSA Y-Bk	4.5	2.4	6.39	p=0.896	p=0.002
IPD Y-Bk	2.2	1.3	2.7	p≤0.001
C Y-Bk	4.15	3.5	5.2
MSA R-G	2.72	2.7	3.1	p=0.249	p=0.358
IPD R-G	1.85	1.4	2.2	p≤0.001
C R-G	3	2.65	3.6
MSA B-Y	3.34	1.9	3.9	p=0.216	p≤0.001
IPD B-Y	1.2	0.95	1.55	p≤0.001
C B-Y	2.55	1.9	3
	Latency
MSA Y-Bk	61	61	66	p=0.586	p=0.461
IPD Y-Bk	64.5	58	73.5	p=0.108
C Y-Bk	61	56	68
MSA R-G	75	70	86	p=0.955	p=0.871
IPD R-G	76	68	85	p=0.792
C R-G	76	70.5	77
MSA B-Y	76.5	65	78	p=0.508	p=0.011
IPD B-Y	85	79.5	91	p≤0.001
C B-Y	71	70	75.5