STATS: Descriptive Statistics

2.1 Summarizing Categorical Data

“nonoverlapping classes”.

Frequency Distribution

Relative Frequency and Percent Frequency Distributions

Bar Charts & Pie Charts

2.2 Summarizing Quantitative Data

Frequency Distribution

The three steps necessary to define the classes for a frequency distribution with quantitative data are:

1. Determine the number of nonoverlapping classes.
   • 5~20 classes. (depends on the size of the data)
2. Determine the width of each class.
   • we recommend that the width be the same for each class.
   • Approximate class width 􏰔 = Largest data value 􏰀- Smallest data value / Number of classes (can be rounded for convenience)
3. Determine the class limits.
   (optional: class midpoint).

Relative Frequency and Percent Frequency Distributions

Dot Plot

Histogram

• Left/Right/Symmetric skew

Cumulative Distributions

(<= upper limit of each class)

Ogive

2.3 Exploratory Data Analysis: The Stem-and-Leaf Display

2.4 Crosstabulations and Scatter Diagrams

Crosstabulations