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chi squared

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The chi squared test is used to compare characteristics of more than two groups (t test would be an appropriate test for 2 characteristics). Using the tables of chi squared will gives the probability of features being due to chance.

The Technique:

  • deal in numbers, not percentages or proportions
  • produce an expected result - total up the results and divide by the number of results
  • Chi squared is equal to the sum of the values of:


( Observed number - Expected number) squared


expected number


(Squaring copes with the problem of negative results).

In the tables need then to allow for degrees of freedom (see degrees of freedom)