(Slide 1)

Lecture 3: Displaying Data

Chapter 2, Whitlock and Schulter, 2nd Ed

Key questions:

What makes a good graph?

What makes a bad graph?

Types of graphs for types of different data

(Slide 2)

Basics Rules of plotting data

1) Show the raw data if possible

2) Show distributional info if possible

3) ALWAYS Include error bars around means

4) ALWAYS Include error bars around means

5) Make patterns in the data easy to see

6) Represent magnitude honestly

7) Draw graphical elements clearly

8) Include a legend and label things clearly

(Slide 3)

Plotting Rule #1: Show the raw data

Compare the information content of these two graphs

(Slide 3.5)

Plotting Rule #1: Show the Data

Multiple datasets can result in the exact same barplot & errorbars

Bar plots – even with error bars – therefore reveals very little about the data


(slide 4)

Plotting Rule #2: Show distributional information

Distributional info can be displayed by plotting the raw data or by using boxplots

(slide 5)

Plotting Rule #3 & 4: Alwys use error bars for means

Means MUST always have an estimate of uncertainty around them

The range doesn’t count!

Typically use “standard error” OR “confidence interval”

Rarely use “standard deviaiton”

(Slide 6)

Plotting Rule #5: Make Patterns Easy to See

Keep it as simple as possible

Add labels, annotations etc.

Use both color AND pattern/shape to distinguish groups

Avoid 3D

Use color-blind friendly palettes

Don’t use most of the fancy stuff in Excel!

3D barplots

(Slide 6.5)

Plotting Rule #5: Make Patterns Easy to See example

(Slide 7)

Plotting Rule #6: Represent Magnitudes Honestly

This plot emphasizes a certain aspect of data

Some critics think this is desceptive