symbolic expression specifying the outcome (continuous)
and grouping variable (factor). See lm() for details.
data
optional data frame containing the variables in the model.
subset
an optional vector specifying a subset of observations to be
used in the fitting process.
na.action
a function which indicates what should happen when the data
contain ‘NA’s. See lm() for details.
bars
a logical value indicating whether confidence interval
bars should be plotted. Defaults to TRUE.
p
confidence level for error bars. Defaults to 0.95.
minsd
minumum permitted value for the standard deviation within
each factor level. Any standard deviation estimates smaller than
minsd will be replaced with minsd. Defaults to 0.
minbar
minumum allowed value for bar ends. If specified,
values smaller than minbar will be replaced with
minbar.
maxbar
maximum allowed value for bar ends. If specified,
values larger than maxbar will be replaced with
maxbar.
xlab
x-axis label.
ylab
y-axis label.
mean.labels
either a logical value indicating whether the circles
representing the group means should be replaced with text giving the
actual mean values or a vector containing labels to use
instead. Defaults to FALSE.
ci.label
a logical value indicating whether text giving the
actual interval end values should be placed at the end of each
confidence interval bar. Defaults to FALSE.
n.label
a logical value indicating whether text giving the number of
observations in each group should should be added to the plot.
text.n.label
Prefix text for labeling observation counts.
Defaults to "n=".
digits
number of significant digits to use when displaying
mean or confidince limit values.
col
color of cicles marking group means. Default is "black".
barwidth
linewidth of interval bars and end marks. Default is
1.
barcol
color of interval bars and end marks. Default is
"blue".
connect
either a logical value indicating whether the means of
each group should be connected by a line, or a list of vectors giving the
index of bars that should be connected by a line. Defaults to TRUE.
ccol
color of lines used to connect means. Defaults to the
same color as "col".
legends
vector containing strings used to label groups along
the x axis. Defaults to group names.
xaxt
A character which specifies the axis type. Specifying ‘"n"’
causes an axis to be set up, but not plotted.
use.t
a logical value indicating whether the t distribution
should be used to compute confidence intervals. If TRUE, the
default, a t distribution will the correct number of degrees of
freedom for each group be used. If FALSE, the a normal
distribution will be used.
# show comparison with boxplot
data(state)
plotmeans(state.area ~ state.region)
# show some color and mean labels
plotmeans(state.area ~ state.region,
mean.labels=TRUE, digits=-3,
col="red", connect=FALSE)
# show how to specify which means should be connected
plotmeans(state.area ~ state.region, connect=list(1:2, 3:4),
ccol="red", pch=7 )
# more complicated example showing how to show an interaction
data(esoph)
par(las=2, # use perpendicular axis labels
mar=c(10.1,4.1,4.1,2.1), # create enough space for long x labels
mgp=c(8,1,0) # move x axis legend down to avoid overlap
)
plotmeans(ncases/ncontrols ~ interaction(agegp , alcgp, sep =" "),
connect=list(1:6,7:12,13:18,19:24),
barwidth=2,
col="dark green",
data=esoph,
xlab="Age Group and Alcohol Consumption",
ylab="# Cases / # Controls",
main=c("Fraction of Cases for by Age and Alcohol Consumption",
"Ile-et-Vilaine Esophageal Cancer Study")
)
abline(v=c(6.5, 12.5, 18.5), lty=2)