Chi square test
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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

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Chi square test

Chi Square Test

Gitanjali Batmanabane


At the end of this session you will be able to

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.


Chi square test

Know thyself

Why does he keep saying this all the time?


Chi square test

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

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

Associations and Causal Associations

Relationship

between variables

Not statistically

associated

Statistically

associated

Non-causal

Causal

Indirectly

causal

Directly

causal


Chi square test

Contingency (2X2) table

  • Enter number of subjects – not percentages, ratios, averages etc.,

  • Each subject can be entered only once


Chi square test

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


Chi square test

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

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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