Unformatted text preview: eder staircase: Schroeder Can you see both directions? Two groups saw this figure and reported Two One group had no distractions The other group counted backwards by 3s The while viewing the figure while how long it took them to see the reverse. how Results Results
Group
Control 2 5 6 8 9 13 15 21 42 Experimental 4 10 11 12 14 17 85 98 ∞
This is why we can’t do a ttest! MannWhitney U analyses MannWhitney
Scores Scores in order in 2 4 5 6 8 9 10 11 12 13 14 15 17 21 42 85 98 ∞ Group Group ID ID 1 2 1 1 1 12 2 2 1 2 1 2 1 1 2 2 2 Rank 1 2 3 4 5 67 8 9 10 11 12 13 14 15 16 17 18 # Times Times A1 before A2 A2 # Times Times A2 before A1 A1 9 8888 5 4 3 3 8 4 4 4 3 2 MannWhitney U analyses MannWhitney UA1 = 9+8+8+8+8+5+4+3+3 = 56 UA2 = 8+4+4+4+3+2 = 25 Or use formula UA2 = n1n2 UA1
UA2 = 9*956 = 8156 = 25 Use smaller value in test MannWhitney U hypotheses MannWhitney H0: The population distribution of A1
scores is identical to the pop. dist. of A2 scores scores scores H1: The pop. dist. of A1 scores is not
identical to the pop. dist. of A2 scores identical MannWhitney U hypothesis testing MannWhitney Red Alert! This test is different! If Uobs < Ucrit Reject H0, accept H1 If Uobs > Ucrit (p. 505506, Tables C8.A and crit
8.B) 8.B) Fail to reject H0, do not accept H1 Ucrit=17, Uobs=25 Fail to reject H0, do not accept H1 Computational formula Computational UA1 = nA1nA2+ nA1(nA1+1)  Σ RA1 A1 A1
2 UA2 = n1n2 UA1 Where nA1=number of scores in group A1 nA2=number of scores in group A2 Σ RA1=sum of ranks assigned to scores in =sum group A1 group Example Example Will receiving an alcohol education Will
program result in reduced estimated daily alcohol consumption? alcohol A1: 0.31, 0.53, 0.58, 0.14, 0.16, 0.52, 0.53, A1: 0.02 0.02 A2: 0.41, 0.63, 1.14, 0.21, 0.89, 0.55, 0.89, A2: 0.91, 0.08, 0.59 0.91, Summary Summary Nonparametric tests are appropriate Nonparametric
when parametric (normal distribution) tests cannot or should not be used. cannot Contingency table (chisquare) tests are of Contingency the form ∑ (OE)/E where E is the “expected” number under the null hypothesis. hypothesis. Rank tests are for continuous data when Rank and are functions of the ranks. and...
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This note was uploaded on 11/30/2009 for the course HP 400m at USC.
 '07
 Nezami,Borovay

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