Chi squared test

Question 1

What does the Chi squared test check for

Answer 1

association between 2 categorical variables. Calculates the frequencies that would be expected if no association->compares observed frequencies with expected values->if observed frequencies are very different=association

Question 2

how to calculate the degrees of freedom for chi squared

Answer 2

(no. of rows-1)x(no. of columns-1)

Question 3

Should you use frequency or % for chi squared test

Answer 3

frequency

Question 4

Which estimates to use for 2x2 table in chi squared test

Answer 4

risk difference: p1-p2, use if actual size of difference is of interest
relative risk: p1/p2, use if relative difference is of interest, easier to interpret than OR but do not use for case control studies
Odds ratio: (p/(1-p))//(p2/(1-p2)) use for case control studies, approximately equal to relative risk when outcome is rare.Can be misinterpreted when outcome more common

Question 5

Null hypothesis for chi squared

Answer 5

In the population where the samples come, there is no association between the 2 variables

Question 6

Assumption of chi squared

Answer 6

large sample test, at least 80% of expected frequencies must be greater than 5. For 2x2 test, all frequencies>5