Gitanjali Batmanabane Chi Square Test Gitanjali Batmanabane

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.

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

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?

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

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

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

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

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

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.