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# Chi Square Test - PowerPoint PPT Presentation

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. Know thyself.

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### Chi Square Test

Gitanjali Batmanabane

• 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?

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?

• Test of proportions

• Non parametric test

• Dichotomous variables are used

• Tests the association between two factors

e.g. treatment and disease

gender and mortality

Relationship

between variables

Not statistically

associated

Statistically

associated

Non-causal

Causal

Indirectly

causal

Directly

causal

• 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.

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.

Total

25

30

25

30

55

Total

Assumptions / Limitations used estrogens. Out of 30 women without uterine cancer 5 claimed to have used estrogens.

• 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.