Table 3.

Results of Wilcoxon and Kruskal–Wallis rank sums tests comparing historical (1846–1916) and 2015 Plantago specimens. Each study site includes pooled leaf tissue from several specimens and represents one replicate (n = 4) for each time period.

	Wilcoxon 2-sample rank sums test			Kruskal–Wallis 1-way rank sums test
Element	S	Z	P	χ2	df	P
Cu	15	−0.72	0.47	0.75	1	0.39
Pb	12	−0.59	0.11	3.00	1	0.08
Zn	16	−0.43	0.67	0.33	1	0.56

Note: df = degrees of freedom; S = score sum; Z = test statistic.