Chapter 2 Summary Statistics And Data Science 188 (188)

Statistics and data science 188 Organising and visualizing variables
Chapter 2
Introduction

In this chapter the following will be covered:
• How to organise and visualise categorical variables.
• How to organise and visualise numerical variables.
• How to summarise a mix of variables.
• How to avoid making common errors when organising and visualising variables.



Tabular and visual summaries
- Summaries guide further exploration and facilitate decision making
- Visual summaries enable rapid review of larger amounts of data
o and show possible patterns
- Often the Organise and Visualize stages occur concurrently


Summary Table
- Tallies the frequencies or percentages of items in a set of categories so differences can be identified
-
Contingency Table
- To study patterns between two or more categorical variables
- Cross tabulates tallies
- Looks at joint distributions
- For two variables the tallies for one variable are located in the rows and the tallies forthe second variable
are located in the columns.

TALLYING
CATEGORICAL DATA




1 categorical variable 2 categorical variables




Summary table Contingency table

, Visual summaries
enable rapid review of larger
amounts of data show
possible significant patterns.




VISUALISING
CATEGORICAL DATA


Summary table for 1
categorical variable




o Bar Chart
o Has gaps (vs no gaps in a histogram)
o Is easiest to understand for the average person
o Pareto Chart
o To display categorical data on a nominal scaleA vertical bar chart
• Categories are shown in descending order of frequency
o A cumulative polygon is shown in the same graph