Contingency tables

Contingency Tables Fundamentals

  • A Contingency table is a type of table that displays the frequency distribution of multiple categorical variables.
  • They are often used in statistical analysis to establish the relationship between two categorical variables.
  • It’s a vital tool in the Chi-Squared test, where it’s used to display the expected and observed frequencies.

How to Construct a Contingency Table

  • Identify the two variables you are focusing on; these will constitute the rows and columns of your table.
  • Calculate the total frequency of each variable, which should be placed in the final row or column of the table.
  • Each cell in the table represents the frequency of a particular combination of the two variables.
  • The sum of the frequencies in any row or column should equate to the total frequency mentioned earlier.

Contingency Tables in Chi-Squared Tests

  • A contingency table can be used to carry out a Chi-Squared test of independence.
  • The Chi-Squared test is used to determine if there is a significant association between the two categorical variables.
  • The expected frequency for each cell in a Chi-Squared test is calculated as (Row Total x Column Total) / Grand Total.

Interpreting Contingency Tables

  • Contingency tables provide a basic visual representation of the relationship between variables.
  • If there is a significant difference between the observed and expected frequencies in each cell of the table (i.e., your Chi-Squared test is significant), it suggests that the variables are not independent.
  • Always remember to interpret statistical findings in context, considering the limitations and potential confounding variables of the study from which your data was collected.