Chapter 4 Displaying and Describing Categorical Data 1 Frequency Tables a Shows the number of visits cases for each category and records totals and category names i Names of the categories label each row when number of categories gets too large lump together values of the variable into an others category ii Relative Frequency Tables Displays values as percentages in order to display the fractions or proportions of the data in each category 1 Divide the counts by the total number of cases b Helps to describe the distribution of a categorical variable b c they name the possible categories and tell how frequently each occurs 2 Charts value it represents a Area Principle The area occupied by a part of the graph should correspond to the magnitude of the b Bar Charts Displays the distribution of a categorical variable showing the counts for each category next to each other for easy comparison i Replace the counts with percentages creating a Relative Frequency Bar Chart to draw attention c Pie Charts Show the whole group of cases as a circle give impressions about how the whole group is d Always check the Categorical Data Condition Ensure that the data are counts or percentages of to the relative proportions partitioned into smaller groups individuals in categories i Also make sure that categories do not overlap so that no individual is counted in two categories 1 If categories overlap percentages will not add up to 100 3 Contingency Tables a A table that shows how individuals are distributed along each variable depending on or contingent on the value of the other variable i Margins of tables give totals ii Marginal Distribution The frequency distribution of either one of the variables in the margin iii Each cell of a contingency table any intersection of a row and column of the table gives the count for a combination of values of the two variables b Most statistics programs offer a choice of total percent row percent or column percent i Total Percent The proportion of the total contained in the cell of a frequency table ii Row Percent The proportion of each row contained in the cell of a frequency table iii Column Percent The proportion of each column contained in cell of a frequency table c Conditional Distributions The distribution of a variable restricting the Who to consider only a smaller d When the distribution of one variable is the same for all categories of another we say that the variables i Aka No association between the two variables a Treats each bar as the whole and then divides it proportionally into segments corresponding to the group of individuals are independent 4 Segmented Bar Charts percentage in each group 5 Simpson s Paradox Compare percentages within each level rather than across levels a Combine comparable measures for comparable individuals
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