Displaying and Describing Categorical Data Chapter 3

Terms Frequency table: Categories and counts Distribution: lists the frequencies of each category Distribution: lists the relative frequencies of each category Contingency Table: The frequencies or relative frequencies of a chart.

Terms Marginal Distribution: the totals found on the margins of the chart Conditional distribution: the distribution of one row or column of a contingency table. Independence: two variables are independent if the conditional distribution of one variable is the same as the conditional distribution of the other

Three Rules of Data Analysis First, make a picture!

Or you could

Why? Pictures reveal things charts don’t. Patterns can be revealed that are not readily apparent from the numbers. Pictures are the easiest way to explain to others about the data

To Make a Graph Make piles. Organize the data into like groups Make a frequency table Make a relative frequency table by finding the percentages

Make a Graph Probably a bar chart graphing the frequencies or... A pie chart to graph the relative frequencies Beware of the area principle. Stay 2-D

To Make a Graph of Categorical Data ThInk  Check W’s  Identify the variables  Check to see if categories overlap  Data are counts

To Make a Graph of Categorical Data Show  Select the appropriate graph to compare categories  Bar Graph for frequencies  Pie Chart for relative frequencies (percents)  Stacked bar graph can be used instead of a pie chart

To Make a Graph of Categorical Data Tell  Interpret the results  Describe the results in the context of the problem  Answers are sentences not numbers