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STAT 301 Lab

Lab 12: Analysis of Two-Way Tables

T.A.: Yixuan Qiu

Two-Way Table

  • Studies the association between two categorical variables

Percentage Table

  • Divide each cell by the total count

Joint, Marginal, Conditional

  • Joint: percentage of a combination of the two factors (look for the key word "and")
  • Marginal: percentage of a single factor
  • Conditional: percentage of a single factor given that we know the value of the other factor

Example

  • What percentage of students have low physical activity and high fruit consumption? (Joint)

Example

  • What percentage of students have moderate physical activity? (Marginal)

Example

  • What percentage of students have low fruit consumption within the group of moderate physical activity? (Conditional)
    • 17.4% / 37.4% = 46.5%

The Chi-square Test

  • Test whether the two factors have association

Condition to Use Chi-square Test

  • For tables larger than 2x2

    • The average of the expected counts is 5 or more and the smallest expected count is 1 or more

  • For 2x2 tables

    • All 4 expected cell counts are 5 or more

Enter Data in SPSS

  • Remember to do the WEIGHT CASES

Last Words

  • Thanks for your hard work in this lab
  • You are all GREAT!