SiegelTukeyTest: Siegel-Tukey Test For Equality In Variability

Description Usage Arguments Details Value Author(s) References See Also Examples

Description

Non-parametric Siegel-Tukey test for equality in variability. The null hypothesis is that the variability of x is equal between two groups. A rejection of the null hypothesis indicates that variability differs between the two groups. SiegelTukeyRank returns the ranks, calculated after Siegel Tukey logic.

Usage

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
SiegelTukeyTest(x, ...)

## Default S3 method:
SiegelTukeyTest(x, y, adjust.median = FALSE,
                alternative = c("two.sided", "less", "greater"),
                mu = 0, exact = NULL, correct = TRUE, conf.int = FALSE,
                conf.level = 0.95, ...)

## S3 method for class 'formula'
SiegelTukeyTest(formula, data, subset, na.action, ...)


SiegelTukeyRank(x, g, drop.median = TRUE)

Arguments

x, y

numeric vector of data values. Non-finite (e.g. infinite or missing) values will be omitted.

g

a vector or factor object giving the group for the corresponding elements of x.

adjust.median

Should between-group differences in medians be leveled before performing the test? In certain cases, the Siegel-Tukey test is susceptible to median differences and may indicate significant differences in variability that, in reality, stem from differences in medians. Default is FALSE.

alternative

a character string specifying the alternative hypothesis, must be one of "two.sided" (default), "greater" or "less". You can specify just the initial letter.

mu

a number specifying an optional parameter used to form the null hypothesis. See Details.

exact

a logical indicating whether an exact p-value should be computed. This is passed directly to wilcox.test.

correct

a logical indicating whether to apply continuity correction in the normal approximation for the p-value.

conf.int

a logical indicating whether a confidence interval should be computed.

conf.level

confidence level of the interval.

formula

a formula of the form lhs ~ rhs where lhs gives the data values and rhs 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 NAs. Defaults to getOption("na.action").

drop.median

logical, defining whether the median of the combined samples should be left out, ensuring that there's an even number of elements (which is a requirement of the Siegel-Tukey test). Defaults to TRUE.

...

further arguments to be passed to or from methods.

Details

The Siegel-Tukey test has relatively low power and may, under certain conditions, indicate significance due to differences in medians rather than differences in variabilities (consider using the argument adjust.median). Consider also using mood.test or ansari.test.

Value

A list of class htest, containing the following components:

statistic

Siegel-Tukey test (Wilcoxon test on tie-adjusted Siegel-Tukey ranks, after the median adjustment if specified).

p.value

the p-value for the test

null.value

is the value of the median specified by the null hypothesis. This equals the input argument mu.

alternative

a character string describing the alternative hypothesis.

method

the type of test applied

data.name

a character string giving the names of the data.

Author(s)

Daniel Malter, Tal Galili <tal.galili@gmail.com>, Andri Signorell <andri@signorell.net>
published on: https://www.r-statistics.com/2010/02/siegel-tukey-a-non-parametric-test-for-equality-in-variability-r-code/

References

Siegel, S., Tukey, J. W. (1960): A nonparametric sum of ranks procedure for relative spread in unpaired samples. Journal of the American Statistical Association.

Sheskin, D. J. (2004): Handbook of parametric and nonparametric statistical procedures 3rd edition. Chapman and Hall/CRC. Boca Raton, FL.

See Also

mood.test, ansari.test, wilcox.test, LeveneTest

Examples

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
# Duller, S. 183
x <- c(12, 13, 29, 30)
y <- c(15, 17, 18, 24, 25, 26)
SiegelTukeyTest(x, y)
SiegelTukeyTest(x, y, alternative="greater")

# Duller, S. 323
old <- c(870,930,935,1045,1050,1052,1055)
new <- c(932,970,980,1001,1009,1030,1032,1040,1046)
SiegelTukeyTest(old, new, alternative = "greater")
# compare to the recommended alternatives
mood.test(old, new, alternative="greater")
ansari.test(old, new, alternative="greater")

# Bortz, S. 250
x <- c(26.3,26.5,26.8,27.0,27.0,27.2,27.3,27.3,27.4,27.5,27.6,27.8,27.9)
id <- c(2,2,2,1,2,2,1,2,2,1,1,1,2)-1
SiegelTukeyTest(x ~ id)


# Sachs, Angewandte Statistik, 12. Auflage, 2007, S. 314
A <- c(10.1,7.3,12.6,2.4,6.1,8.5,8.8,9.4,10.1,9.8)
B <- c(15.3,3.6,16.5,2.9,3.3,4.2,4.9,7.3,11.7,13.1)
SiegelTukeyTest(A, B)



### 1
x <- c(4,4,5,5,6,6)
y <- c(0,0,1,9,10,10)
SiegelTukeyTest(x, y)

### 2
# example for a non equal number of cases:
x <- c(4,4,5,5,6,6)
y <- c(0,0,1,9,10)
SiegelTukeyTest(x, y)

### 3
x <- c(33, 62, 84, 85, 88, 93, 97, 4, 16, 48, 51, 66, 98)
id <- c(0,0,0,0,0,0,0,1,1,1,1,1,1)
SiegelTukeyTest(x ~ id)

### 4
x <- c(177,200,227,230,232,268,272,297,47,105,126,142,158,172,197,220,225,230,262,270)
id <- c(rep(0,8),rep(1,12))
SiegelTukeyTest(x ~ id, adjust.median=TRUE)

### 5
x <- c(33,62,84,85,88,93,97)
y <- c(4,16,48,51,66,98)
SiegelTukeyTest(x, y)

### 6
x <- c(0,0,1,4,4,5,5,6,6,9,10,10)
id <- c(0,0,0,1,1,1,1,1,1,0,0,0)
SiegelTukeyTest(x ~ id)

### 7
x <- c(85,106,96, 105, 104, 108, 86)
id <- c(0,0,1,1,1,1,1)
SiegelTukeyTest(x ~ id)

Example output

	Siegel-Tukey-test for equal variability

data:  x and y
ST = 10, p-value = 0.009524
alternative hypothesis: true ratio of scales is not equal to 1


	Siegel-Tukey-test for equal variability

data:  x and y
ST = 10, p-value = 0.004762
alternative hypothesis: true ratio of scales is greater than 1


	Siegel-Tukey-test for equal variability

data:  old and new
ST = 34, p-value = 0.002622
alternative hypothesis: true ratio of scales is greater than 1


	Mood two-sample test of scale

data:  old and new
Z = 2.8666, p-value = 0.002075
alternative hypothesis: greater


	Ansari-Bradley test

data:  old and new
AB = 18, p-value = 0.001573
alternative hypothesis: true ratio of scales is greater than 1


	Siegel-Tukey-test for equal variability

data:  x by id
ST = 35.5, p-value = 0.6842
alternative hypothesis: true ratio of scales is not equal to 1

Warning message:
In wilcox.test.default(ranks0, ranks1, alternative = alternative,  :
  cannot compute exact p-value with ties

	Siegel-Tukey-test for equal variability

data:  A and B
ST = 134.5, p-value = 0.02324
alternative hypothesis: true ratio of scales is not equal to 1

Warning message:
In wilcox.test.default(ranks0, ranks1, alternative = alternative,  :
  cannot compute exact p-value with ties

	Siegel-Tukey-test for equal variability

data:  x and y
ST = 57, p-value = 0.003601
alternative hypothesis: true ratio of scales is not equal to 1

Warning message:
In wilcox.test.default(ranks0, ranks1, alternative = alternative,  :
  cannot compute exact p-value with ties

	Siegel-Tukey-test for equal variability

data:  x and y
ST = 15, p-value = 0.01141
alternative hypothesis: true ratio of scales is not equal to 1

Warning message:
In wilcox.test.default(ranks0, ranks1, alternative = alternative,  :
  cannot compute exact p-value with ties

	Siegel-Tukey-test for equal variability

data:  x by id
ST = 24, p-value = 0.202
alternative hypothesis: true ratio of scales is not equal to 1


	Siegel-Tukey-test for equal variability

data:  x by id
ST = 106, p-value = 0.09788
alternative hypothesis: true ratio of scales is not equal to 1


	Siegel-Tukey-test for equal variability

data:  x and y
ST = 24, p-value = 0.202
alternative hypothesis: true ratio of scales is not equal to 1


	Siegel-Tukey-test for equal variability

data:  x by id
ST = 21, p-value = 0.003601
alternative hypothesis: true ratio of scales is not equal to 1

Warning message:
In wilcox.test.default(ranks0, ranks1, alternative = alternative,  :
  cannot compute exact p-value with ties

	Siegel-Tukey-test for equal variability

data:  x by id
ST = 4, p-value = 0.2667
alternative hypothesis: true ratio of scales is not equal to 1

DescTools documentation built on June 17, 2021, 5:12 p.m.