Table 1.

Mean distance to nearest neighbor of same group and permutation test for nonrandom clustering

Spectral region, cm−1	Mean distance*			Mean rank†
	Observed	Random permutation	P value	Observed	Random permutation	P value
1750–700	12.2	12.8	0.1	2.0	3.0	0.01
1750–1500	12.3	12.3	0.5	2.4	3.0	0.09
1499–1310	5.9	6.5	0.02	1.6	3.0	<0.001
1309–1175	6.7	6.5	0.7	3.0	3.0	0.5
1174–1000	13.2	15.0	0.02	2.0	3.0	0.01
999–700	6.9	7.4	0.1	2.3	3.0	0.05

Distance is expressed as a percent difference between spectra; 1000 permutations were performed for each spectral subregion. 

^*Mean Euclidean distance to nearest neighbor in the same group expressed as a percent. 

^†Mean rank of Euclidean distance of each spectrum to nearest neighbor in the same group.