Lecture 7

Question 1

χ2 – the (chi square) goodness of fit test

Answer 1

Compares the expected number of observations in each category with the observed number of observations. This calculates an error score for each category, and tells us how big of a surprise (or mistake) the null hypothesis made when we used it to predict our observed frequencies

Question 2

How can χ2 be used?

Answer 2

Goodness of fit tests and to determine if two or more variables are independent on a single population (E.g. smoking and lung cancer)

Question 3

Degrees of Freedom for goodness of fit

Answer 3

The number of possible choices minus 1

Question 4

Degrees of freedom for a test of association

Answer 4

(number of rows-1) x (number or columns-1)