Purpose
Exploration
Testing hypotheses is a critical part of the scientific process.
But…you need to understand your data first.
- What are some relationships, how are variables distributed, etc.
Visualizing your data can go a long way to helping you explore your data.
Preattentive Processing
We pick up on visual cues much quicker than reading (i.e., what catches our eye).
- That is why entire disciplines are devoted to visual processing.
Some things hit us pretty quickly:
- color - hue & intensity
- shape
- space/density
- line width & orientation
- size
Preattentive Processing In Action
Correlation Matrix
| mpg | cyl | disp | hp | drat | wt | qsec | vs | |
|---|---|---|---|---|---|---|---|---|
| mpg | 1.00 | -0.85 | -0.85 | -0.78 | 0.68 | -0.87 | 0.42 | 0.66 |
| cyl | -0.85 | 1.00 | 0.90 | 0.83 | -0.70 | 0.78 | -0.59 | -0.81 |
| disp | -0.85 | 0.90 | 1.00 | 0.79 | -0.71 | 0.89 | -0.43 | -0.71 |
| hp | -0.78 | 0.83 | 0.79 | 1.00 | -0.45 | 0.66 | -0.71 | -0.72 |
| drat | 0.68 | -0.70 | -0.71 | -0.45 | 1.00 | -0.71 | 0.09 | 0.44 |
| wt | -0.87 | 0.78 | 0.89 | 0.66 | -0.71 | 1.00 | -0.17 | -0.55 |
| qsec | 0.42 | -0.59 | -0.43 | -0.71 | 0.09 | -0.17 | 1.00 | 0.74 |
| vs | 0.66 | -0.81 | -0.71 | -0.72 | 0.44 | -0.55 | 0.74 | 1.00 |
Corrplot
Heat Map
Inference
Currently, most journals "need" to see test statistics to know if there is a relationship.
- The golden p-value is the driver of science!
Not everything needs a test statistic to tell you that a real relationship exists (or not).
Interocular Traumatic Impact
Maybe A Better Fit
Principles And Properties
What Was And What Should Never Be
Color
Color is generally used for the following:
Groups
Intensity
Only use color when it is actually doing something to aid interpretation.
Color - Groups
Color - Intensity
Color - Brewer Palettes
Color - Tol Palettes
Color - Few Palettes
Size
Much like color, size can convey very distinct ideas:
Value size
Frequency
You need to be very explicit to which you are referring!
Size
Shape
Shape is a bit more limited than color and size.
It really only helps to denote group membership.
And only does well when things are sparse.
Shape - Linetypes
Where We Have Trouble…
Shape - Points
Alpha
- No, we are not talking about Cronbach.
- We probably all know about the RGB color model.
- But…did you know that it can have a fourth channel?
- Alpha!
- Alpha is essentially transparency.
- 0 is completely translucent
How Does Alpha Help
We are frequently fortunate enough to have a considerable amount of data.
Depending on what type of plotting we want to do, we could run into problems very quickly.
Alpha
Jitter
If you have ever held a jumping bean or drank too much coffee, you might already know about jitter.
Jitter is useful if we have some minor overplotting issues.
- It would not be a good fix for what we just saw.
Looks Pretty Clear…
After Jittering
An Alternative
Other Ideas
Small Multiples/Faceting
We often want to compare a plot over several different levels.
We have already seen ways to use color and other items to make groups distinct.
If you want to be daring, though, there are other methods.
Small Multiples/Faceting
Multiple Relationships – Very Powerful
Combining Features
We just saw a glimpse about how we can use multiple principles to convey information.
- We had a two-variable facet, size, and density estimates.
Combining Features
Other Combinations
Tips (And Maybe Tricks)
Grid Lines
The default is always some version of "No".
When To Use Grid Lines
Use for:
- Large plots
- Make differences clear
- Comparing values on categorical scales
- Narrowing focus
When you do use them, they should be very faint.
Large Plots
Make Differences Clearer
Comparing Categorical Scale
Narrowing Focus
Interactivity
Given the confines of publishing, we cannot always default to interactive visualization.
There are journals and outlets making progress on this front!
Journal of Computational and Graphical Statistics anyone?
However, it is a great place to start when exploring data.
- It is also great for disseminating information on the web.
Making Old Trouble Disappear
Grid lines…who needs them?
We All Remember This Monster
The Clutter Is Strong With This One
Still A Better Version
Important People
Mike Bostok – D3
Cynthia Brewer – Color Brewer
William Cleveland – Pioneer (Citation Champ)
Stephen Few – All Things Viz
Michael Friendly – Psychologist and Viz Expert
Paul Tol – Physicist and Viz Expert
Edward Tufte – Information Display
Hadley Wickham – Reigning Data Science Heavyweight Champion
Leland Wilkinson – The Grammar of Graphics