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 |

`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]