Association

# Association - Association Click to edit Master subtitle...

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Click to edit Master subtitle style Association 4/13/2011

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Announcements n Chapter 12 HW due on Monday n Research talk this Friday, noon, Gambrell 250
What do we Mean by Association? n Association implies a relationship between two variables. n If you change the X, you will get a change in Y. n Relationship is not necessarily causal.

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Measures of Association n Can describe the relationship between two variables in terms of ¨ Direction (positive or negative) ¨ Form (linear, nonlinear, etc) ¨ Strength ¨ Conditional relationships
Association n Ways of describing association depends upon data types: ¨ Scatterplots ¨ Tables ¨ Correlation ¨ Regression

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Scatterplots n Scatterplot is a visual way of presenting a relationship. n Only work with ratio / interval data.

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Scatterplots n Simply plot, for each case, the values of X on the x axis and Y on the y axis. Dependent variable Independent variable

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Cross tabulation/Contingency Tables n Frequency table with 2 variables ¨ Y categories are rows ¨ X categories are columns n Usually best for nominal and ordinal data
Example n Y= 2000 presidential vote choice ¨ Bush, Gore, other n X= party affiliation ¨ Republican, Democrat, other

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Table 1. 2000 Presidential Vote Choice, by Party Respondent Party Identification Vote Choice Dem Ind Rep Total Gore 505 37 45 587 Bush 55 37 435 527 Other 16 11 15 42 Total 576 85 495 1156 Source: American National Election Study, 2000
Table 1. 2000 Presidential Vote Choice, by Party Respondent Party Identification Vote Choice Democrat Independent Republican Total Gore 505 37 45 587 Bush 55 37 435 527 Other 16 11 15 42 Total 576 85 495 1156 Column Marginal Frequency Row Marginal Frequency n

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Contingency w/ % n Divide cell frequency by column marginal.
Contingency w/ % Respondent Party Identification Vote Choice Democrat Independent Republican Total Gore 88% 44% 9% 51% Bush 10% 44% 88% 46% Other 3% 13% 3% 4% Total 101%* 101% 100% 101% Source: American National Election Study, 2000 *Percentages may not add to 100, due to rounding.

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With % and Marginals Respondent Party Identification Vote Choice Democrat Independent Republican Total Gore 88% 44% 9% 51% (587) Bush 10% 44% 88% 46% (527) Other 3% 13% 3% 4% (42) Total 101%* 101% 100% 101% (576) (85) (495) (1156)
Making Tables n Include descriptive and shorthand title n Provide Source of Data n Make Y Rows and X Columns n Clearly Label Rows and Columns

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Making Tables n In cells, report % of column n Report Row Freq. and % n Report Column Freq. and % n Round Percentages n Report Total Observations (n)
For Interval or Ratio Data n Make categories n Loses information

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n How can assess association with a cross tab? n What would perfect association look like? n
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