ANOVA: Analysis of Variance

Description

Abbreviation: av, av.brief

Analysis of variance with graphics.

Can also be called from the more general model function.

Usage

ANOVA(my.formula, dframe=mydata, 
         brief=FALSE, digits.d=4, ...)
av(my.formula, ...)
av.brief(my.formula, brief=TRUE, ...)

Arguments

my.formula

Standard R formula for specifying a model. For example, for a response variable named Y and two predictor variables, X1 and X2, specify the corresponding linear model as Y ~ X1 + X2.

dframe

The default name of the data frame that contains the data for analysis is mydata, otherwise explicitly specify.

brief

Extent of displayed results.

digits.d

For the Basic Analysis, it provides the number of decimal digits. For the rest of the output, it is a suggestion only.

...

Other parameter values for R function lm which provides the core computations.

Details

One-way ANOVA with Tukey HSD and plot based on the R functions aov, TukeyHSD, and provides summary statistics for each level. Two-factor ANOVA also provides an interaction plot of the means with interaction.plot as well as a table of means and other summary statistics.

Examples

Run this code

# create simulated data, no population mean difference
# X has two values only, Y is numeric
# put into a data frame
n <- 12
X <- sample(c("Group1","Group2"), size=n, replace=TRUE)
Y <- rnorm(n=n, mean=50, sd=10)
mydata <- data.frame(X,Y)

# analyze data with formula version
# variable names and levels of X are automatically obtained from data
# although data frame not attached, reference variable names directly
ANOVA(Y ~ X)
# short name
av(Y ~ X)

# variable of interest is in a data frame which is not the default mydata
# access the data frame in the lessR dat.twogroup data set
# although data not attached, access the variables directly by their name
data(datTwoGroup)
ANOVA(ShipTime ~ Supplier, dframe=datTwoGroup)

# two-factor ANOVA with replications and interaction
ANOVA(breaks ~ wool * tension, dframe=warpbreaks)

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