Math 106: Elements of Statistics
Graphically Displaying Data
January 20, 2016
Learning Objectives:






Know how to differentiate categorical from numeric variables, and within numeric
variables, be able to differentiate between continuous and discrete variables
Understand how and when to use various types of graphical displays to show univariate
distributions: bar charts, pie charts, stem-and-leaf plots, dot plots, histograms, box plots
Know how "bin sizes" might affect stem-and-leaf plots, dot plots, and histograms.
Understand how and when to use various types of graphical displays to show bivariate
distributions: scatterplots, stacked bar charts, etc.
Know how to use R to create the graphs listed above!
Be able to discuss the shape, center, and spread of a distribution (of a univariate set of
data)
Note: You should save your work to your H: drive, NOT to the C: drive of the computer on which
you’re working!
The data from our class dataset can be found at
P:\Data\MATH\Snipes\Statistics_S16\Datasets\ClassDataS16.csv
The scripts we went through today were
P:\Data\MATH\Snipes\Statistics_S16\RScripts\GraphIntroNum.R
P:\Data\MATH\Snipes\Statistics_S16\RScripts\GraphIntroCat.R
Homework Assignment (in lieu of book problems)
Due Friday Jan. 22
For homework, make the following graphs by adjusting the code from the scripts. Unless
otherwise noted, you should be using the class dataset.
Paste your graphs in the following text, along with the code you used to produce each, and
answer the questions below.
Displaying Numerical Variables
Univariate Data

Make a dotplot of the variable Age.mos.
1. What is apparent here? We will discuss this at length – it is one of the most
misunderstood topics in data analysis.


Make a stem-and-leaf plot of Wingspan.in. Paste your graph in this document, along
with the code you used to produce the graph. Describe this distribution (center, spread,
shape).
Load the data set P:\Data\MATH\Snipes\Statistics_S16\Datasets\obits.csv, which
provides the age in years of the deceased as listed in the obituaries for four weeks of The
Columbus Dispatch. Make a histogram1 of the variable Age at Death.
1. Describe the center, range, and shape of the distribution.
Bivariate Data
What information do you get from the following chart?

Make a scatterplot of Height.in. vs. RightFoot.in.
CHOOSE YOUR OWN ADVENTURE:

Poke around in the data. Make one chart of your choosing (not one from the class demo,
nor from this worksheet) and include it below.
Part 2: Displaying Categorical Variables SAVE FOR LATER
Univariate (just one variable!) Data

Make a pie chart of the variable Varsity from our class dataset.

Make a bar chart of the variable Award. What percentage of our class would prefer a
Nobel Prize?
Bivariate (two variables!) Data

Make a comparative bar chart of Varsity vs. Award.
1. Discuss your observations.
1
Note that changing “bin sizes” for both dotplots and histograms changes how the data looks! Check out the
following website for a cool demonstration of this fact!
http://www.amstat.org/publications/jse/v6n3/applets/histogram.html