Chi square test
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Chi Square Test PowerPoint PPT Presentation


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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

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

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

  • 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

  • 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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