This function performs a Mann-Whitney-U-Test (or Wilcoxon rank sum test,
see wilcox.test
and wilcox_test
)
for x
, for each group indicated by grp
. If grp
has more than two categories, a comparison between each combination of
two groups is performed.
The function reports U, p and Z-values as well as effect size r
and group-rank-means.
mwu(x, dv, grp, distribution = "asymptotic", weight.by = NULL, out = c("txt", "viewer", "browser"))
x | A (grouped) data frame. |
---|---|
dv | Name of the dependent variable, for which the mean value, grouped
by |
grp | Factor with the cross-classifying variable, where |
distribution | Indicates how the null distribution of the test statistic should be computed.
May be one of |
weight.by | Name of variable in |
out | Character vector, indicating whether the results should be printed
to console ( |
(Invisibly) returns a data frame with U, p and Z-values for each group-comparison as well as effect-size r; additionally, group-labels and groups' n's are also included.
This function calls the wilcox_test
with formula. If grp
has more than two groups, additionally a Kruskal-Wallis-Test (see kruskal.test
)
is performed.
Interpretation of effect sizes, as a rule-of-thumb:
small effect >= 0.1
medium effect >= 0.3
large effect >= 0.5
data(efc) # Mann-Whitney-U-Tests for elder's age by elder's dependency. mwu(efc, e17age, e42dep)#> #> # Mann-Whitney-U-Test #> #> Groups 1 = independent (n = 65) | 2 = slightly dependent (n = 224): #> U = 7635.000, W = 41905.000, p = 0.003, Z = -3.020 #> effect-size r = 0.100 #> rank-mean(1) = 117.46 #> rank-mean(2) = 152.99 #> #> Groups 1 = independent (n = 65) | 3 = moderately dependent (n = 304): #> U = 8692.000, W = 68265.000, p < 0.001, Z = -4.273 #> effect-size r = 0.142 #> rank-mean(1) = 133.72 #> rank-mean(3) = 195.96 #> #> Groups 1 = independent (n = 65) | 4 = severely dependent (n = 297): #> U = 7905.500, W = 65703.000, p < 0.001, Z = -5.096 #> effect-size r = 0.169 #> rank-mean(1) = 121.62 #> rank-mean(4) = 194.60 #> #> Groups 2 = slightly dependent (n = 224) | 3 = moderately dependent (n = 304): #> U = 54664.500, W = 139656.000, p = 0.008, Z = -2.647 #> effect-size r = 0.088 #> rank-mean(2) = 244.04 #> rank-mean(3) = 279.58 #> #> Groups 2 = slightly dependent (n = 224) | 4 = severely dependent (n = 297): #> U = 51007.500, W = 135981.000, p < 0.001, Z = -4.386 #> effect-size r = 0.146 #> rank-mean(2) = 227.71 #> rank-mean(4) = 286.11 #> #> Groups 3 = moderately dependent (n = 304) | 4 = severely dependent (n = 297): #> U = 87819.500, W = 180901.000, p = 0.083, Z = -1.732 #> effect-size r = 0.057 #> rank-mean(3) = 288.88 #> rank-mean(4) = 313.41 #> #> # Kruskal-Wallis-Test #> #> chi-squared = 38.476 #> df = 3 #> p < 0.001