The magnification to be used for plotting symbols.
min.cex
Minimal magnification for plotting symbols.
max.cex
Maximal magnification for plotting symbols.
pch
The plotting symbol used for individual studies.
col
A vector with colour of plotting symbols.
bg
A vector with background colour of plotting symbols (only
used if pch in 21:25).
lty
The line type for the meta-regression line.
lwd
The line width for the meta-regression line.
col.line
Colour for the meta-regression line.
studlab
A logical indicating whether study labels should be
printed in the graph. A vector with study labels can also be
provided (must be of same length as the numer of studies in the
meta-analysis then).
cex.studlab
The magnification for study labels.
pos
A position specifier for study labels (see text).
offset
Offset for study labels (see text).
regline
A logical indicating whether a regression line should
be added to the bubble plot.
axes
A logical indicating whether axes should be printed.
box
A logical indicating whether a box should be printed.
...
Graphical arguments as in par may also be
passed as arguments.
Details
A bubble plot can be used to display the result of a
meta-regression. It is a scatter plot with the treatment effect for
each study on the y-axis and the covariate used in the
meta-regression on the x-axis. Typically, the size of the plotting
symbol is inversely proportional to the variance of the estimated
treatment effect (Thompson & Higgins, 2002).
Argument cex specifies the plotting size for each individual
study. If this argument is missing the weights from the
meta-regression model will be used (which typically is a random
effects model). Use weight="fixed" in order to utilise
weights from a fixed effect model to define the size of the plotted
symbols (even for a random effects meta-regression). If a vector
with individual study weights is provided, the length of this vector
must be of the same length as the number of studies.
Arguments min.cex and max.cex can be used to define
the size of the smallest and largest plotting symbol. The plotting
size of the most precise study is set to max.cex whereas the
plotting size of all studies with a plotting size smaller than
min.cex will be set to min.cex.
For a meta-regression with more than one covariate. Only a scatter
plot of the first covariate in the regression model is shown. In
this case the effect of the first covariate adjusted for other
covariates in the meta-regression model is shown.
For a factor or categorial covariate separate bubble plots for each
group compared to the baseline group are plotted.