Scatter Plot
A scatter plot pairs up values of two quantitative variables in a data set and display them as geometric points inside a Cartesian diagram.
Example
In the data set faithful, we pair up the eruptions and waiting values in the same observation as (x,y) coordinates. Then we plot the points in the Cartesian plane. Here is a preview of the eruption data value pairs with the help of the cbind function.
> waiting = faithful$waiting # the waiting interval
> head(cbind(duration, waiting))
duration waiting
[1,] 3.600 79
[2,] 1.800 54
[3,] 3.333 74
[4,] 2.283 62
[5,] 4.533 85
[6,] 2.883 55
Problem
Find the scatter plot of the eruption durations and waiting intervals in faithful. Does it reveal any relationship between the variables?
Solution
We apply the plot function to compute the scatter plot of eruptions and waiting.
> waiting = faithful$waiting # the waiting interval
> plot(duration, waiting, # plot the variables
+ xlab="Eruption duration", # x−axis label
+ ylab="Time waited") # y−axis label
Answer
The scatter plot of the eruption durations and waiting intervals is as follows. It reveals a positive linear relationship between them.
Enhanced Solution
We can generate a linear regression model of the two variables with the lm function, and then draw a trend line with abline.
