Table 2. Results of the Mann-Whitney U-test to determine if El Niño/Southern Oscillation extremes significantly affected flow at five gaging stations.
[U1 and U2 are lower and upper sample values of the test statistic U. U0.05 and U0.95 are the lower and upper critical values of U used to accept or reject the null hypothesis HO: median of population 1 (F1) = median of population 2 (F2). The alternative hypothesis H1: median of F1 < median of F2 is supported by U1 values less than U0.05 and U2 values greater than U0.95. See Tamhane and Dunlop (2000) for discussion of technique]
|
Gaging station
|
U1
|
U2
|
Decision
|
|
Mississippi River at St. Louis
|
89
|
135
|
Accept HO
|
Ohio River at Metropolis
|
85
|
139
|
Accept HO
|
Mississippi River at Vicksburg
|
95
|
145
|
Accept HO
|
Rio Grande at Embudo
|
39
|
201
|
Reject HO
|
Rio Grande at Presidio1
|
12
|
118
|
Reject HO
|
|
1At level of significance = 0.05, U0.5 = 38 and U0.95 = 92. Presidio comparison for 1930-97; all others for 1915-97.
|
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