| test.levene {misty} | R Documentation |
Description
This function performs Levene's test for hom*ogeneity of variance across twoor more independent groups.
Usage
test.levene(formula, data, method = c("median", "mean"), conf.level = 0.95, hypo = TRUE, descript = TRUE, plot = FALSE, violin.alpha = 0.3, violin.trim = FALSE, box = TRUE, box.alpha = 0.2, box.width = 0.2, jitter = TRUE, jitter.size = 1.25, jitter.width = 0.05, jitter.height = 0, jitter.alpha = 0.2, gray = FALSE, start = 0.9, end = 0.4, color = NULL, xlab = NULL, ylab = NULL, ylim = NULL, breaks = ggplot2::waiver(), title = "", subtitle = "", digits = 2, p.digits = 3, as.na = NULL, write = NULL, append = TRUE, check = TRUE, output = TRUE)Arguments
formula | a formula of the form |
data | a matrix or data frame containing the variables in theformula |
method | a character string specifying the method to compute thecenter of each group, i.e. |
conf.level | a numeric value between 0 and 1 indicating the confidencelevel of the interval. |
hypo | logical: if |
descript | logical: if |
plot | logical: if |
violin.alpha | a numeric value indicating the opacity of the violins. |
violin.trim | logical: if |
box | logical: if |
box.alpha | a numeric value indicating the opacity of the boxplots. |
box.width | a numeric value indicating the width of the boxplots. |
jitter | logical: if |
jitter.size | a numeric value indicating the |
jitter.width | a numeric value indicating the amount of horizontal jitter. |
jitter.height | a numeric value indicating the amount of vertical jitter. |
jitter.alpha | a numeric value indicating the opacity of the jittereddata points. |
gray | logical: if |
start | a numeric value between 0 and 1, graphical parameter tospecify the gray value at the low end of the palette. |
end | a numeric value between 0 and 1, graphical parameter tospecify the gray value at the high end of the palette. |
color | a character vector, indicating the color of the violinsand the boxes. By default, default ggplot2 colors areused. |
xlab | a character string specifying the labels for the x-axis. |
ylab | a character string specifying the labels for the y-axis. |
ylim | a numeric vector of length two specifying limits of thelimits of the y-axis. |
breaks | a numeric vector specifying the points at which tick-marksare drawn at the y-axis. |
title | a character string specifying the text for the title forthe plot. |
subtitle | a character string specifying the text for the subtitlefor the plot. |
digits | an integer value indicating the number of decimal placesto be used for displaying results. |
p.digits | an integer value indicating the number of decimal placesto be used for displaying the p-value. |
as.na | a numeric vector indicating user-defined missing values,i.e. these values are converted to |
write | a character string naming a text file with file extension |
append | logical: if |
check | logical: if |
output | logical: if |
Details
Levene's test is equivalent to a one-way analysis of variance (ANOVA) with theabsolute deviations of observations from the mean of each group as dependentvariable (center = "mean"). Brown and Forsythe (1974) modified theLevene's test by using the absolute deviations of observations from the median(center = "median"). By default, the Levene's test uses the absolutedeviations of observations from the median.
Value
Returns an object of class misty.object, which is a list with followingentries:
call | function call |
type | type of analysis |
formula | formula of the current analysis |
data | data frame specified in |
plot | ggplot2 object for plotting the results |
args | specification of function arguments |
result | list with result tables, i.e., |
Author(s)
Takuya Yanagida takuya.yanagida@univie.ac.at
References
Brown, M. B., & Forsythe, A. B. (1974). Robust tests for the equality ofvariances. Journal of the American Statistical Association, 69,364-367.
Rasch, D., Kubinger, K. D., & Yanagida, T. (2011). Statistics in psychology- Using R and SPSS. John Wiley & Sons.
See Also
aov.b, test.t, test.welch
Examples
dat <- data.frame(y = c(2, 3, 4, 5, 5, 7, 8, 4, 5, 2, 4, 3), group = c(1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3))# Example 1: Levene's test based on the median with 95% confidence intervaltest.levene(y ~ group, data = dat)# Example 2: Levene's test based on the arithmetic mean with 95% confidence intervaltest.levene(y ~ group, data = dat, method = "mean")# Example 3: Levene's test based on the median with 99% confidence intervaltest.levene(y ~ group, data = dat, conf.level = 0.99)## Not run: # Example 4: Write results into a text filetest.levene(y ~ group, data = dat, write = "Levene.txt")# Example 5: Levene's test based on the median with 95# plot resultstest.levene(y ~ group, data = dat, plot = TRUE)# Load ggplot2 packagelibrary(ggplot2)# Save plot, ggsave() from the ggplot2 packageggsave("Levene-test.png", dpi = 600, width = 5, height = 6)# Levene's test based on the median with 95# extract plotp <- test.levene(y ~ group, data = dat, output = FALSE)$plotp# Example 6: Extract dataplotdat <- test.levene(y ~ group, data = dat, output = FALSE)$data# Draw violin and boxplots in line with the default setting of test.levene()ggplot(plotdat, aes(group, y, fill = group)) + geom_violin(alpha = 0.3, trim = FALSE) + geom_boxplot(alpha = 0.2, width = 0.2) + geom_jitter(alpha = 0.2, width = 0.05, size = 1.25) + theme_bw() + guides(fill = "none")## End(Not run)[Package misty version 0.6.5 Index]
