Year

Mean

Mann-Whitney U

Wilcoxon

Z-Statistics

Asymptotic

Significant

(2 Tailed)

Sen’s Estimator

Number of Samples

1971-1980

1981-1990

8.8

12.2

33

88

−1.285

0.199

1.437

10

10

1991-2000

2001-2010

11

10

45

100

−0.378

0.705

−0.0232

10

10