BOXPLOTS
There are other plots in R that can be very useful - a classic one for examining data is a box plot.
In this lesson you will learn how to plot bar graphs in R. Load the data HERE into a table named data. Name the columns subject, group, and rt.
Generating a boxplot if very easy. Simply use:
boxplot(data$rt~data$group)
You should see something that looks like this.
Now, what is important with a box plot is what information is shown. The line in the middle of each "box" is the median score for the group. The bottom of the box represents the first quartile (or 25th percentile) score. The top of the box represents the third quartile (or 75th percentile) score. The bottom and the top of the "error bars" represent the minimum and maximum scores respectively.
What of the circles? The circles represent outlying scores - these are scores that the function generating the box plot decides are too extreme to actually be in the group. Let's verify this quickly with the first group:
group1 = data$rt[data$group == 1]
median(group1)
min(group1)
max(group1)
You will note the values returned for min and max are the circles shown on the boxplot.
If you want to see what the numbers the box plot is computing - try this:
stuff = boxplot(data$rt~data$group)
stuff
What you should see here is that the box plot is returning all of the information in the plot and more - even the confidence intervals for the groups.
For a list of all the properties of a boxplots, use
?boxplot
Note, all of the classic plot properties such as titles, axis labels, and axis limits can be set.
In this lesson you will learn how to plot bar graphs in R. Load the data HERE into a table named data. Name the columns subject, group, and rt.
Generating a boxplot if very easy. Simply use:
boxplot(data$rt~data$group)
You should see something that looks like this.
Now, what is important with a box plot is what information is shown. The line in the middle of each "box" is the median score for the group. The bottom of the box represents the first quartile (or 25th percentile) score. The top of the box represents the third quartile (or 75th percentile) score. The bottom and the top of the "error bars" represent the minimum and maximum scores respectively.
What of the circles? The circles represent outlying scores - these are scores that the function generating the box plot decides are too extreme to actually be in the group. Let's verify this quickly with the first group:
group1 = data$rt[data$group == 1]
median(group1)
min(group1)
max(group1)
You will note the values returned for min and max are the circles shown on the boxplot.
If you want to see what the numbers the box plot is computing - try this:
stuff = boxplot(data$rt~data$group)
stuff
What you should see here is that the box plot is returning all of the information in the plot and more - even the confidence intervals for the groups.
For a list of all the properties of a boxplots, use
?boxplot
Note, all of the classic plot properties such as titles, axis labels, and axis limits can be set.