Chapter 2

> Four different ways to visually describe just one variable
• Frequency table
• Grouped frequency table
• Frequency histograms
• Frequency polygon

Histogram for the Frequency Table of
Graduate Advisors

Histogram for the Grouped Frequency Table of TV Pacing
Index Data

Frequency Polygons as Another Graphing Option for the TV Pacing Index Data

> How old are the students in our class?
• Construct a frequency table; grouped frequency table; histogram; frequency polygon
> What is the best method of presentation for our data?

Shapes of Distributions
> Normal distributions: Specific frequency distribution
• Bell shaped
• Symmetrical
• Unimodal

The Normal Distribution

> When our data are not symmetrical
• Positive: tail to the right
> May represent floor effects
• Negative: tail to the left
> May represent ceiling effects
• Memory hint: skew is where the tail is

Two Kinds of Skew

Everyone Improves

Helps the High Performers

Helps the Low Performers