# mood.test

##### Mood Two-Sample Test of Scale

Performs Mood's two-sample test for a difference in scale parameters.

- Keywords
- htest

##### Usage

`mood.test(x, …)`# S3 method for default
mood.test(x, y,
alternative = c("two.sided", "less", "greater"), …)

# S3 method for 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

`"two.sided"`

(default),`"greater"`

or`"less"`

all of which can be abbreviated.- formula
a formula of the form

`lhs ~ rhs`

where`lhs`

is a numeric variable giving the data values and`rhs`

a factor with two levels giving the corresponding groups.- data
an optional matrix or data frame (or similar: see

`model.frame`

) containing the variables in the formula`formula`

. By default the variables are taken from`environment(formula)`

.- 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

`NA`

s. Defaults to`getOption("na.action")`

.- …
further arguments to be passed to or from methods.

##### Details

The underlying model is that the two samples are drawn from \(f(x-l)\) and \(f((x-l)/s)/s\), 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:

the value of the test statistic.

the p-value of the test.

a character string describing the alternative hypothesis. You can specify just the initial letter.

the character string `"Mood two-sample test of scale"`

.

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.
10.2307/1266427.

##### See Also

`fligner.test`

for a rank-based (nonparametric) k-sample
test for homogeneity of variances;
`ansari.test`

for another rank-based two-sample test for a
difference in scale parameters;
`var.test`

and `bartlett.test`

for parametric
tests for the homogeneity in variance.

##### Examples

`library(stats)`

```
# NOT RUN {
## Same data as for the Ansari-Bradley 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)
# }
```

*Documentation reproduced from package stats, version 3.6.2, License: Part of R 3.6.2*