May 26, 2017 - Choosing the right chart to represent your data can be a daunting .... bar chart. Group A. Group B categorical count conditional bar chart count.
How to Choose a Chart A Statistically Motivated Guide
Andy Grogan-Kaylor May 26, 2017
How to Choose a Chart Choosing the right chart to represent your data can be a daunting process. I believe that a starting point for this thinking is some basic statistical thinking about the type of variables that you have. At the broadest level, variables may be conceptualized as categorical variables, or continuous variables. • categorical variables represent unordered categories like gender, or religious affiliation. • continuous variables represent a continuous scale like a mental health scale, or a measure of neighborhood quality. Once we have discerned the type of variable that have, there are two followup questions we may ask before deciding upon a chart strategy: • Is our graph about one thing at a time? – How much of x is there? – What is the distribution of x? • Is our graph about two things at a time? – What is the relationship of x and y? – How are x and y associated?
A Few Notes A Note About Graph Labels Graphs should have clear titles and labels.
1
Informative Title some other piece of information
Maybe The Title Is Even Your Main Takeaway 1.02 1.01 1.00 0.99 0.98
120
possibly informative key takeaway
110 100 90
informative label goes here
80
Words should be spelled out. Every extra 'dimension' should convey information.
A Note About Software The principles of graphing discussed in this document transcend any particular software package, and could be implemented in many different software packages. The graphs in these particular examples use ggplot2, a graphing library in R. ggplot2 graph syntax can be formidably complex, with a somewhat steep learning curve. More information about ggplot can be found here.
A Note About Graph Colors This document uses colors based upon official University of Michigan colors. Using colors that match the design scheme of your organization may be helpful.
A Simulated Data File of Continuous and Categorical Data The first few observations… x
y
z
u
v
w
66.77 79.99 73.84 188.3 131.5 117.8
107.5 107.2 122.5 295.6 111.9 103
83.95 143 122.2 118.9 76.81 106.8
Group A Group A Group A Group A Group A Group A
Group A Group A Group A Group A Group A Group A
Group A Group A Group A Group B Group A Group A
2
One Thing At A Time
Two Things At A Time
Continuous
Continuous By Categorical
histogram
conditional histogram
150
Group A 100
100
50
count
count
150
50
0
Group B 150 100 50
0
0
0
100
200
300
0
100
continuous
200
density
conditional density Group A
0.008
density
density
0.012
0.004 0.000 100
200
0.015 0.010 0.005 0.000
Group B 0.015 0.010 0.005 0.000
300
100
continuous
200 100
300
conditional boxplot continuous
300
200
continuous
boxplot continuous
300
continuous
300 200 100 Group A
Group B
categorical
150 100 50 0
mean of continuous
mean of continuous
barchart of mean 200
conditional barchart of means 200 150 100 50 0 Group A
Group B
categorical
3
violin plot
conditional violin plot Group A
continuous
continuous
300 200 100
Group B
300 200 100
categorical
dotplot
conditional dotplot Group A
0.75
density
density
1.00
0.50 0.25 0.00 100
200
1.00 0.75 0.50 0.25 0.00
Group B 1.00 0.75 0.50 0.25 0.00
300
100
continuous
200
300
continuous
One Thing At A Time
Two Things At A Time
Categorical
Categorical By Categorical
bar chart
conditional bar chart Group B
count
count
Group A
categorical
categorical
horizontal bar chart
conditional horizontal bar chart categorical
categorical
Group A
Group B
count
count
4
pie chart
conditional pie chart Group A
Group B
categorical
categorical
doughnut chart
conditional doughnut chart Group A
categorical
Group B
categorical
Continuous by Continuous scatterplot with fit line continuous
continuous
scatterplot
continuous
continuous
smoother count 20 15 10 5
continuous
continuous
hexagon plot
continuous
continuous
5
area plot
contour plot level continuous
continuous
0.00016 0.00012 0.00008 0.00004
continuous
continuous
Graphics made with the ggplot2 graphing library created by Hadley Wickham. Available online at https://agroganweb.wordpress.com/data-visualization-dataviz/
How to Choose a Chart by Andrew Grogan-Kaylor is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License. You are welcome to download and use this handout in your own classes, or work, as long as the handout remains properly attributed. Last updated: May 26 2017 at 15:10
