Psychology 513: Advanced Research Methods

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Psychology 513 Advanced Research Methods

• Regression with Categorical Variables

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Overview

• Regression can accommodate continuous variables
  and categorical variables
• Need to code the categorical variables in order
  to use them in regression
• We will focus on dummy coding

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Dummy Codes

• Assign ones and zeros
• of dummy variables of categories 1
• Males 0, Females 1
• Base category 0

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Example Two categories

• Regress empathy scores on sex
• Dummy code sex
• Males 0, Females 1
• Regression equation
• Yhat 3.30 3.60 X R20.58

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Summary Table for Regression
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Analyzing the data with ANOVA
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More Than Two Categories

• Political Affiliation Independent, Democrat,
  Republican
• Create two dummy variables
• Independent (0,0)
• Democrat (1,0)
• Republican (0,1)