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Chapter 4

# 73-100 Chapter Notes - Chapter 4: Marginal Distribution, Contingency Table, Bar Chart

Department
Business
Course Code
MSCI 1000
Professor
Peter Miller
Chapter
4

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CHAPTER 4 â€“ Displaying and Describing Categorical Data
Make a picture
- display data ! help see what you are not likely to see in table ! help plan approach to
analysis
- shows important features, patterns and relationships
- reveals extraordinary (or possible wrong) data
- best way to report data to others
Frequency Tables â€“ shows number of cases (ex. website visits) for each category and records
totals and category names (ex. provinces)
- describe the distribution of a categorical variable â€“ name possible categories and tell how
frequently each occurs.
Relative frequency table â€“ displays percentages, rather than the counts, of each of the value in
each category
Charts:
- The area principle â€“ the area occupied by a part of the graph should correspond to the
magnitude of the value it represents
- Bar charts â€“ displays the distribution of a categorical variable, showing the counts for each
category next to each other for easy comparison
- more accurate visual impression of the distribution
- common base, freestanding, spaces in-between
- horizontal or vertical
- Relative frequency bar chart â€“ replacing counts with percentages, draws attention to
proportion
- Pie Charts â€“ severe perceptual problems, hard to interpret â€“ try not to use them!
Categorical Data Condition â€“ that the data are counts or percentages of individuals in
categories
- make sure categories donâ€™t overlap
** best perception of â€“ positions of common scale (ex. plot or bar graph), comparing 2 separate
images with same scale, length
worst perception â€“ volume, colour, angles, area
Contingency tables â€“ shows how individuals are distributed along each variable, depending on
(contingent on), the value of the other variable
- marginal distribution â€“ in a contingency table, the distribution of either variable alone.
The counts or percentages are the totals found n the margins (usually the right-most column
or bottom row) of the table.
- each cell â€“ gives the count for a combination of values of the two variables
- total percentage, row percentage, column percentage
Conditional distribution â€“ shows the distribution of one variable for just those cases that satisfy
a condition on another
Independent variable â€“ when the distribution of one variable is the same for all categories of
another, in a contingency table (no association between the variables)
Segmented Bar Charts â€“ treats each bar as the â€œwhole and divides it proportionally into
segments corresponding to the percentage in each group
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