Displaying Distributions Chapters 10 and...

Displaying Distributions

Chapters 10 and 11

Feb 2, 2013

Exploratory Data Analysis

Appropriate Graphics

Basic Shapes of Histograms

Uses of Histograms

1.0 Exploratory Data Analysis

Here we analyze the data on it’s own terms withoutmaking any assumptions.

The idea is to organize and summarize so as to uncoverany underlying patterns in the data.

Our focus is also on understanding the distribution ofthe variables.

DefinitionThe distribution of a variable tells us what values ittakes and how often it takes these values.

1.1 Impact of No Child Left Behindsource: N.Y. Times

1. What is the observational unit in the graphic?2. What are the variables being measured?3. What do we uncover?

1.2 Tremors in Italysource: Nature

1. What is the observational unit in the graphic?2. What are the variables being measured?3. What do we uncover?

1.3 King County Housing Marketsource: seattlebubble.com

King County S.F.H. Sales Histogram

1. What is the observational unit in the graphic?2. What are the variables being measured?3. What do we uncover?

1.4 Income Distributionsource: C.P.S. 2004

1. What is the observational unit in the graphic?

2. What are the variables being measured?

3. What do we uncover?

2.0 Appropriate Graphics

For qualitative variables:

Pie Charts

Bar Graphs

Tables:

For quantitative variables:

Histograms

Stem-and-leaf plots (skip: pp 226-229)

3.0 Basic Shapes of Histogramssource: Prof. Morita

4.0 Uses of Histograms

Histograms may be used to study one distribution.

Outlier? Shape? Center? Spread?

4.1 Uses of Histograms

Histograms may be used to compare different distributions.

Blood pressure of pill users and non-users (women age 25-29)

In one figure the use of the pill adds 10mm to the bloodpressures. In the other the pill adds about 10%. Which iswhich and why?