Using R for Introductory Statistics 3.2

[This article was first published on Digithead's Lab Notebook, and kindly contributed to R-bloggers]. (You can report issue about the content on this page here)
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

…continuing my sloth-like progress through John Verzani’s Using R for Introductory Statistics. Previous installments: Chapters 1 and 2 and 3.1.

Comparing independent samples

Boxplots provide a visual comparison between two or more distributions. For problem 3.8, we’re asked to compare the reaction times of cell phone users verses a control group, to test the theory that using a cell phone while driving is a bad idea. Comparing the centers and spreads can be done with the following boxplot.

boxplot(time ~ control, reaction.time, names=c('control', 'phone'),
  ylab='reaction time in seconds',
  main='Reaction time with cell phone usage')

The tilde operator, ~, is used to define a model formula, which is something I aspire to understand someday but currently am clueless about.

Looking at the same data as a density plot might give a better picture of each distribution.

  main="Reaction time with cell phone usage",
  xlab="reaction time in seconds")
lines(density(reaction.time$time[reaction.time$control=='C']), lty=2)

Still, boxplots are nice because they give you a sense of the center, range, dispersion, and skew of a sample in a compact and comparable form. Plus, you can plot several boxplots side-by-side.

boxplot(morley$Speed ~ morley$Expt,
  col='light grey', xlab='Experiment #',
  ylab="speed (km/s minus 299,000)",
  main="Michelson–Morley experiment")
mtext("speed of light data")
abline(h=sol, col='red')

Problem 3.11 uses data from the 1887 Michelson-Morley experiments attempting to find variations in the speed of light due to earth’s motion through the aether, believed at the time to be the medium through which light waves traveled. The correct value for the speed of light is shown in red.

And finally, whadya know, this stuff came in handy for some (probably not very rigorous) performance analysis.

To leave a comment for the author, please follow the link and comment on their blog: Digithead's Lab Notebook. offers daily e-mail updates about R news and tutorials about learning R and many other topics. Click here if you're looking to post or find an R/data-science job.
Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.

Never miss an update!
Subscribe to R-bloggers to receive
e-mails with the latest R posts.
(You will not see this message again.)

Click here to close (This popup will not appear again)