Table 1.

Ten replicates weighing 1, 2, 3, 4 and 5 mg of hair from the same subject (50 samples in all) were extracted, measured and total within-assay coefficient of variation calculated

Weight of hair sample (n = 10 for each weight)	Coefficient of variation %
1 mg	46.2
2 mg	16.1
3 mg	12.4
4 mg	13.6
5 mg	7.9