Contingency tables

Question 1

What is a chi squared test and what are its requirements? (4)

Answer 1

Compares observed value to expected values

Requirements:

• Data is frequencies or counts
• Study groups are independent
• Value of cell expected should be more than 5 in more than 80% of cells and not zero

Question 2

What is absolute risk and how is it calculated?

Answer 2

The probability of something happening in a sample or population

number of people experiencing event / total number of people in the sample or population

Question 3

What is relative risk / risk ratio and how is it calculated?

Answer 3

Ratio of absolute risk of outcome in one group to that of another group

absolute risk of group 1 / absolute risk of group 2

Question 4

What is odds and how is it calculated?

Answer 4

Chance of an event occurring compared to it not occurring

number of people with event / number of people without event

Question 5

What is odds ratio?

Answer 5

Ratio of odds of an outcome for one group compared to the odds of that outcome of a second group

odds for group 1 / odds for group 2

Question 6

When are risk and odds used? (2)

Answer 6

Where we have binary exposure and binary outcome