mood.test {stats}  R Documentation 
Mood TwoSample Test of Scale
Description
Performs Mood's twosample test for a difference in scale parameters.
Usage
mood.test(x, ...)
## Default S3 method:
mood.test(x, y,
alternative = c("two.sided", "less", "greater"), ...)
## S3 method for class 'formula'
mood.test(formula, data, subset, na.action, ...)
Arguments
x , y 
numeric vectors of data values. 
alternative 
indicates the alternative hypothesis and must be
one of 
formula 
a formula of the form 
data 
an optional matrix or data frame (or similar: see

subset 
an optional vector specifying a subset of observations to be used. 
na.action 
a function which indicates what should happen when
the data contain 
... 
further arguments to be passed to or from methods. 
Details
The underlying model is that the two samples are drawn from
f(xl)
and f((xl)/s)/s
, respectively, where l
is a
common location parameter and s
is a scale parameter.
The null hypothesis is s = 1
.
There are more useful tests for this problem.
In the case of ties, the formulation of Mielke (1967) is employed.
Value
A list with class "htest"
containing the following components:
statistic 
the value of the test statistic. 
p.value 
the pvalue of the test. 
alternative 
a character string describing the alternative hypothesis. You can specify just the initial letter. 
method 
the character string 
data.name 
a character string giving the names of the data. 
References
William J. Conover (1971), Practical nonparametric statistics. New York: John Wiley & Sons. Pages 234f.
Paul W. Mielke, Jr. (1967). Note on some squared rank tests with existing ties. Technometrics, 9/2, 312–314. doi:10.2307/1266427.
See Also
fligner.test
for a rankbased (nonparametric) ksample
test for homogeneity of variances;
ansari.test
for another rankbased twosample test for a
difference in scale parameters;
var.test
and bartlett.test
for parametric
tests for the homogeneity in variance.
Examples
## Same data as for the AnsariBradley test:
## Serum iron determination using Hyland control sera
ramsay < c(111, 107, 100, 99, 102, 106, 109, 108, 104, 99,
101, 96, 97, 102, 107, 113, 116, 113, 110, 98)
jung.parekh < c(107, 108, 106, 98, 105, 103, 110, 105, 104,
100, 96, 108, 103, 104, 114, 114, 113, 108, 106, 99)
mood.test(ramsay, jung.parekh)
## Compare this to ansari.test(ramsay, jung.parekh)