Week 11 (Chi-squared)

Question 1

What is Chi square test

Answer 1

Test of association
-Used with categorical variables
-Non-parametric
-Does not make any assumptions

Question 2

How Chi-square works

Answer 2

-If there is no association, the observed values - the frequencies in each cell - do not differ from what we would EXPECT to happen merely by chance.
-But if the observed values are significantly different from the expected values, we can conclude that there is an association between the variables that differs from what we would expect by chance.

Question 3

How to calculate expected values

Answer 3

Row total X Column total divided by Grand total

Question 4

How to calculate chi square ( χ2)

Answer 4

1. Square each O-E value
2. Divide each result by it’s expected value
3. Add up all the results

Question 5

Interpreting Chi Square

Answer 5

Should always be either zero or a positive value
-If it is not zero, then an association exists
-To get p value for significance we need degrees of freedom
-Compare this to a critical value table

Question 6

How to calculate degrees of freedom for chi square

Answer 6

df = (Number of Rows - 1) (Number of Columns - 1)
e.g df = (2-1)(2-1)

1 X 1 = 1

df = 1