CH. 2

Graphical Summaries of Data

Key Definitions

• Variability: Differences in values/categories among individuals.

• Distribution: Reflects the values a variable takes and their frequencies.

• Frequency Table: Summarizes data; applicable for categorical and quantitative variables.

Types of Graphical Summaries

Bar Graphs

• Bars can be vertical/horizontal, with uniform width and spacing.

• Represents frequency or percentage of categories.

• Must include a title, labels, and vertical scale.

Pie Charts

• Circle divided into sectors representing relative frequencies of categories.

• Each sector's size corresponds to the category's frequency.

• Requires a title and legend.

Contingency Tables

• Displays distributions of two categorical variables together.

• Cells indicate counts for combinations of variables.

Conditional Distributions

• Shows distribution of one variable conditional on another.

• Indicates association between variables if distributions differ.

Side-by-Side & Stacked Bar Graphs

• Side-by-side: Compares categories of one variable with another.

• Stacked: One categorical variable is displayed on top of another.

• Both help visualize relationships between variables.

Quantitative Data Representation

Histograms

• Bar graph representation of frequency distribution for quantitative variables.

• No gaps between bars (unless class is empty).

• Class intervals (bins) must cover all observed data values.

Stemplots

• Displays data while maintaining original values, using stems and leaves for visualization.

Dotplots

• Useful for small data sets to show value concentration and gaps.

Time-Series Plots

• Graphs behavior of a variable over time; time on x-axis, variable on y-axis.

• Looks for overall trends and seasonal patterns.