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.
- 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
(Squaring copes with the problem of negative results).
In the tables need then to allow for degrees of freedom (see degrees of freedom)