Add a Vertical Line to the Plot
To add a vertical line to the plot as an overlay in the R Language by using the geom_vline() function. We can add a vertical line in the plot to show the position of zero for better visualization of the data. We can use the xintercept, linetype, color, and alpha argument of the geom_vline() function to customize the position, the shape of the line, color, and transparency of the vertical line respectively.
Syntax:
plot + geom_vline( xintercept, linetype, color, alpha )
Parameter:
- xintercept: determines the position of the line on the x-axis.
- linetype: determines the shape of the line.
- color: determines the color of the line.
- alpha: determines the transparency of the line.
Example: Forest plot with a vertical line at x=0.
R
# create sample data sample_data <- data.frame(study=c('G1', 'G2', 'G3', 'G4', 'G5'), index=1:5, result=c(-.23, -.45, -.16, .6, .65), error_lower=c(-.35, -.59, -.37, -.12, .24), error_upper=c(-.17, -.25, -.03, .82, .91)) #load library ggplot2 library(ggplot2) #create forest plot ggplot(data=sample_data, aes(y=index, x=result, xmin=error_lower, xmax=error_upper)) + geom_point() + geom_errorbarh(height=.1) + scale_y_continuous(labels=sample_data$study)+ geom_vline(xintercept=0, color='green', linetype='dashed', alpha=.8) |
Output:
How to Create a Forest Plot in R?
In this article, we will discuss how to create a Forest Plot in the R programming language.
A forest plot is also known as a blobbogram. It helps us to visualize estimated results from a certain number of studies together along with the overall results in a single plot. It is extensively used in medical research for visualizing a meta-analysis of the results of randomized controlled trials. The x-axis of the plot contains the value of the interest in the studies and the y-axis displays the results from the different trials.
To create a Forest Plot in the R Language, we use a combination of scatter plots along with the error bar. The geom_point() function of the ggplot package helps us to create a scatter plot. To create an error bar plot as an overlay on top of the scatter plot, we use the geom_errorbarh() function. The geom_errorbarh() function is used to draw a horizontal error bar plot.
Syntax:
ggplot(data, aes( y, x, xmin, xmax )) + geom_point() + geom_errorbarh( height )
Parameter:
- data: determines the data frame to be used for plotting.
- x and y: determines the axes variables
- xmin and xmax: determines the x-axis limits
- height: determines the width of the error bar
Example: Basic forest plot.
R
# create sample data sample_data <- data.frame(study=c('G1', 'G2', 'G3', 'G4', 'G5'), index=1:5, result=c(-.23, -.45, -.16, .6, .65), error_lower=c(-.35, -.59, -.37, -.12, .24), error_upper=c(-.17, -.25, -.03, .82, .91)) #load library ggplot2 library(ggplot2) #create forest plot ggplot(data=sample_data, aes(y=index, x=result, xmin=error_lower, xmax=error_upper)) + geom_point() + geom_errorbarh(height=.1) + scale_y_continuous(labels=sample_data$study) |
Output: