Homogeneity of Variance Plot

Description

Oneway analysis of variance makes the assumption that the variances of the groups are equal. Brown and Forsyth, 1974 present the recommended test of this assumption. The Brown and Forsyth test statistic is the F statistic resulting from an ordinary one-way analysis of variance on the absolute deviations from the median. The hovPlot function graphs the components of the Brown and Forsyth test statistic.

Usage

hovPlot(x, data = sys.parent(), method = "bf",  ## x is a formula
        transpose = TRUE, ...)

## users will normally use the formula above and will not call the
## method directly.
hovPlot.bf(x, group,  ## x is the response variable
           y.name = deparse(substitute(x)),
           group.name = deparse(substitute(group)),
           transpose = TRUE, ...)

## users will normally use the formula above and will not call the
## panel function directly.
panel.hov(..., transpose = TRUE)

Arguments

Value

"trellis" object with three panels containing boxplots for each group: The observed data "y", the data with the median subtracted "y-med(y)", and the absolute deviations from the median "abs(y-med(y))" The Brown and Forsyth test statistic is the F statistic resulting from an ordinary one-way analysis of variance on the data points in the third panel.

Author(s)

Richard M. Heiberger <rmh@temple.edu>

References

Heiberger, Richard M. and Holland, Burt (2004b). Statistical Analysis and Data Display: An Intermediate Course with Examples in S-Plus, R, and SAS. Springer Texts in Statistics. Springer. ISBN 0-387-40270-5.

Brown, M.~B. and Forsyth, A.~B. (1974). Robust tests for equality of variances. Journal of the American Statistical Association, 69:364–367.

See Also

aov, hov

Examples

data(turkey)

hov(wt.gain ~ diet, data=turkey)
hovPlot(wt.gain ~ diet, data=turkey)

Results

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
Copyright (C) 2016 The R Foundation for Statistical Computing
Platform: x86_64-pc-linux-gnu (64-bit)

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Type 'demo()' for some demos, 'help()' for on-line help, or
'help.start()' for an HTML browser interface to help.
Type 'q()' to quit R.

> library(HH)
Loading required package: lattice
Loading required package: grid
Loading required package: latticeExtra
Loading required package: RColorBrewer
Loading required package: multcomp
Loading required package: mvtnorm
Loading required package: survival
Loading required package: TH.data
Loading required package: MASS

Attaching package: 'TH.data'

The following object is masked from 'package:MASS':

    geyser

Loading required package: gridExtra
> png(filename="/home/ddbj/snapshot/RGM3/R_CC/result/HH/plot.hov.Rd_%03d_medium.png", width=480, height=480)
> ### Name: plot.hov
> ### Title: Homogeneity of Variance Plot
> ### Aliases: hovPlot hovPlot.bf panel.hov
> ### Keywords: models hplot
> 
> ### ** Examples
> 
> data(turkey)
> 
> hov(wt.gain ~ diet, data=turkey)

	hov: Brown-Forsyth

data:  wt.gain
F = 2.2257, df:diet = 4, df:Residuals = 25, p-value = 0.09506
alternative hypothesis: variances are not identical

> hovPlot(wt.gain ~ diet, data=turkey)
> 
> 
> 
> 
> 
> dev.off()
null device 
          1 
>