Chi-Square Test for Independence

Day 117 - Lesson 11.2

Learning Targets
  • Perform a chi-square test for independence.

  • Choose the appropriate chi-square test in a given setting.

Activity: Are Gender and Favorite Class Independent?
Answer Key:
Activity Link Pic.JPG

There is really nothing new that students need to complete this activity. All of the mechanics of the chi-square test for independence are the same as the chi-square test of homogeneity from yesterday.

How Do I Know Which Chi-square Test?

To help organize their thinking about the three different chi-square tests, students should consider the number of variables and number of populations.

Chi-square test for goodness of fit: 1 variable, 1 population.

Chi-square test for homogeneity: 1 variable, 2+ populations/treatments.

Chi-square test for independence: 2 variables, 1 population.

Context Matters!

To help students remember the difference between the three chi-square tests, urge them to recall the context that we used in class to introduce the test. Here are the contexts that we used in the text:

  1. M&M’S –> Chi-square test for goodness of fit

  2. Gummy bears –> Chi-square test for homogeneity

  3. Gender and favorite class –> Chi-square test for independence

Final Note

The 2016 and 2017 AP Statistics Exams each had a free response question that asked students to do a chi-square test. So this means that it will not be on the 2018 AP Exam (wait…unless each exam is independent of the previous ones).

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