Creating a box plot with whiskers in Stata (or R)

Question

I want to create a boxplot with whiskers. I want to compare several studies. For each study I have

1. mean
2. standard deviation sd
3. name
4. number of observations n

How can I do this in Stata 13 ?

Normally I would type

graph box var

but var is not the mean ........

Answer 1

If all you have from each study is the mean, standard deviation, and number of observations, you cannot possibly generate an accurate boxplot. However, you could assume the outcomes follow a particular distribution (e.g. normal distribution) and plot a boxplot of synthetically generated datasets using those summary statistics:

set.seed(144)
dat <- data.frame(study=c("A", "B", "C"), mean=c(1, 1.5, 1.2), sd=c(1, 2, 3),
                  n=c(40, 100, 12))
synthetic <- do.call(rbind, lapply(split(dat, seq(nrow(dat))), function(row) {
  data.frame(study=row$study, y=rnorm(row$n, row$mean, row$sd))
}))
boxplot(y~study, data=synthetic)

Just to reiterate, this is synthetic data being plotted, assuming a particular form of distribution for the study outcome. If you need to plot the study results, you'll need more information about each study -- the min and max, 25, 50, and 75 quartiles, and any outliers.

Answer 2

Here's a way to do it in R. If you have access to the individual data points, you can do something like the following:

# Fake data
y = rnorm(100)

boxplot(y)

If you only have the summary statistics, you can manually change the values for the box-and-whisker statistics as follows:

plot1 = boxplot(y)
plot1$stats
           [,1]
[1,] -2.1433772
[2,] -0.5599737
[3,]  0.1944167
[4,]  0.6697005
[5,]  2.2113372

The above numbers are in order: lower whisker, lower box, midline, upper box, upper whisker. You can change those numbers to whatever values you have, as follows:

plot1$stats = c(-1.5, -1.2, 0.3, 1.2, 2.6) 

Or change single values as follows:

plot1$stats[2] = -1.2

Then redraw the plot:

boxplot(plot1$stats)

This is all very quick and dirty, but hopefully that will get you started.