test of association: chi-squared

Question 1

what is chi-squared used to test?

Answer 1

difference or association

Question 2

criteria for using chi-squared

Answer 2

• nominal data
• looking for difference
• independent groups (unrelated data)

Question 3

(CS) step 1: 2x2 contingency table

Answer 3

• show observed frequencies in each cell
• calculate the total for each row, each column and the overall total

Question 4

what is the expected frequency?

Answer 4

the frequency that would be expected if there was no difference between the two groups

Question 5

how do you calculate the expected frequency?

Answer 5

(total for row x total for column) / grand total

Question 6

(CS) step 2: table of expected frequencies

Answer 6

include:

• E
• O - E
• (O - E)²
• (O - E)² / E
• ∑(O - E)² / E

Question 7

(CS) step 3: working out the value of x²

Answer 7

x² = (O - E)² / E

Question 8

(CS) step 4: the calculated and critical values

Answer 8

• df = (rows - 1) x (columns - 1)
• if the calculated value of x² is more than the critical value, we reject the null hypothesis and accept the alternative hypothesis