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Gitanjali Batmanabane
Chi Square Test Gitanjali Batmanabane
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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.
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Why does he keep saying this all the time?
Know thyself Why does he keep saying this all the time?
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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?
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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
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Associations and Causal Associations
Relationship between variables Not statistically associated Statistically associated Non-causal Causal Indirectly causal Directly causal
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Contingency (2X2) table Exposure Outcome Yes No
Enter number of subjects – not percentages, ratios, averages etc., Each subject can be entered only once
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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
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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
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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.
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