1. Gitanjali Batmanabane
Chi Square Test
Gitanjali Batmanabane

2. At the end of this session you will be able to:
Prepare a contingency table
Realise which study designs are suitable for applying the chi square test
Understand the assumptions / limitations of the chi square test.

3. Why does he keep saying this all the time?
Know thyself
Why does he keep saying this all the time?

4. No, my son, but I understand something about this “NOT KNOWING”
Excuse me sir, you say “know yourself” all the time but do
YOU KNOW YOURSELF?

5. What is it? Test of proportions Non parametric test
Dichotomous variables are used
Tests the association between two factors
e.g. treatment and disease
gender and mortality

6. Associations and Causal Associations
Relationship
between variables
Not statistically
associated
Statistically
associated
Non-causal
Causal
Indirectly
causal
Directly
causal

7. Contingency (2X2) table Exposure Outcome Yes No
Enter number of subjects – not percentages, ratios, averages etc.,
Each subject can be entered only once

8. Out of 25 women who had uterine cancer, 20 claimed to have used estrogens. Out of 30 women without uterine cancer 5 claimed to have used estrogens.
Exposure
(estrogen)
Outcome (cancer)
Yes No
Total
Total

9. Out of 25 women who had uterine cancer, 20 claimed to have used estrogens. Out of 30 women without uterine cancer 5 claimed to have used estrogens.
Exposure
Outcome
Yes No 20 5 25
Total 25 30 25 30 55
Total

10. Assumptions / Limitations
Data is from a random sample.
A sufficiently large sample size is required (at least 20)
Actual count data (not percentages)
Adequate cell sizes should be present. (>5 in all cells- if less number present apply Yates correction)
Observations must be independent.
Does not prove causality.