Nominal Data

• In related and unrelated t-tests, we compare…

  The means of experimental groups
• What measures of tendency can be calculated for nominal data?

  Mode and Median
• What tests can we conduct using nominal data?

  Chi-Squared and Sign tests
• In a chi-squared test, we start by putting our data into a contingency table.
• What do we calculate in a chi-squared test?

  Chi-squared value
• The bigger the difference between our experimental groups, the bigger the chi-squared value.
• The bigger the chi-squared value, the more likely we are to accept the alternative hypothesis.
• In a given study, a bigger chi-squared value means…

  • We are more likely to reject the null hypothesis.
  • A smaller probability that we’d observe our results, if the null hypothesis is correct
• How to calculate the degrees of freedom in a chi-squared test.


  (number of collums - 1) x (number of rows - 1)
• In a chi-squared test, we reject the hypothesis if the calculated value is greater than or equal to the critical value of chi-squared.
• In the chi-squared test, the degrees of freedom is the number of rows in the contingency table subtract 1 multiplied by the number of columns in the contingency table subtract 1. We reject the null hypothesis if our observed chi-squared value exceeds the critical chi-squared​ value.
• At the same significance level and degrees of freedom, the critical chi-squared​ value is different for a two-tailed test compared to a one-tailed test.
• What experimental design can we use the chi-squared test in?

  Independent groups design - unrelated