Bus Analytics Ch 2

summary table

tallies the frequencies or percentages of items in a set of categories so that you can see differences between categories.

contingency table

Used to study patterns that may exist between the responses of two or more categorical variables.

• Cross tabulates or tallies jointly the responses of the categorical variables.

• For two variables the tallies for one variable are located in the rows and the tallies for the second variable are located in the columns.

ordered array

A sequence of data, in rank order, from the smallest value to the largest value.

▪Shows range (minimum value to maximum value).

▪May help identify outliers (unusual observations).

frequency distribution

a summary table in which the data are arranged into numerically ordered classes.

• ▪must give attention to selecting the appropriate number of class groupings for the table, determining a suitable width of a class grouping, and establishing the boundaries of each class grouping to avoid overlapping.

Why Use a Frequency Distribution

■It condenses the raw data into a more useful form.

■It allows for a quick visual interpretation of the data.

■It enables the determination of the major characteristics of the data set including where the data are concentrated / clustered.

bar chart

visualizes a categorical variable as a series of bars. The length of each bar represents either the frequency or percentage of values for each category.  Each bar is separated by a space called a gap.

pie chart

a circle broken up into slices that represent categories. The size of each slice of the pie varies according to the percentage in each category.

doughnut chart

is the outer part of a circle broken up into pieces that represent categories. The size of each piece of the _____ varies according to the percentage in each category.

• can be used to represent the data from a contingency table.

pareto chart

■Used to portray categorical data (nominal scale).

■A vertical bar chart, where categories are shown in descending order of frequency.

■A cumulative polygon is shown in the same graph.

■Used to separate the “vital few” from the “trivial many.”

side by side bar chart

represents the data from a contingency table

stem and leaf display

organizes data into groups (called stems) so that the values within each group (the leaves) branch out to the right on each row.

• A simple way to see how the data are distributed and where concentrations of data exist.

histogram

A vertical bar chart of the data in a frequency distribution

• no gaps between adjacent bars

• ▪The class boundaries (or class midpoints) are shown on the horizontal axis.

  ▪The vertical axis is either frequency, relative frequency, or percentage.

  ▪The height of the bars represent the frequency, relative frequency, or percentage.

percentage polygon

▪formed by having the midpoint of each class represent the data in that class and then connecting the sequence of midpoints at their respective class percentages.

cumulative percentage polygon (ogive)

displays the variable of interest along the X axis, and the cumulative percentages along the Y axis.

• Useful when there are two or more groups to compare

frequency polygon

Useful When Comparing Two or More Groups

scatter plot

used for numerical data consisting of paired observations taken from two numerical variables.

• One variable’s values are displayed on the horizontal or X axis and the other variable’s values are displayed on the vertical  or Y axis.

• used to examine possible relationships between two numerical variables.

time series plot

used to study patterns in the values of a numeric variable over time.

• Numeric variable’s values are on the vertical axis and the time period is on the horizontal axis.

multidimensional contingency table

is constructed by tallying the responses of three or more categorical variables

• Can be used to discover possible patterns and relationships in multidimensional data that simpler tables and charts would fail to make apparent

• tables should be limited to no more than 3 or 4 variables

Bubble charts

• Extend scatter plots

• Use the size of points (called bubbles) to represent the value of an additional variable

selective summarization

Presenting only part of the data collected.