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Chapter 3 Displaying and Describing Categorical Data

What should we do with categorical data? Make a picture!!

See page 21, Florence Nightingale display that shows causes of soldier's deaths in the Crimean War.

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You can put the data into "piles" and make a frequency table, which records the totals and category names. A relative frequency table displays the percentages rather than the counts.

The area principle: the area occupied by a part of the graph should correspond to the magnitude of the value it represents.

Use a bar chart or pie chart to display the frequency of categorical data.

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Contingency Table ­ shows how the individuals are distributed along each variable, contingent on the value of the other variable.

The marginal distribution is the frequency distribution of one of the variables in the contingency table. The right column of the table is the frequency distribution of the survival variable and the bottom row is the frequency distribution of the class variable.

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Conditional distributions ­ It shows the distribution of one variable for just the individuals who satisfy some condition on another variable.

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Independent ­ When the distribution of one variable is the same for all categories of another in a contingency table.

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Simpson's Paradox ­ When averages are taken across different groups, they can appear to contradict the overall averages.

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Example ­ daytime and nighttime flights

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HW p.41;25,30,35,37 ANS

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HW p.41;25,30,35,37 ANS