Statistics: Chi-square

Chi-square goodness-of-fit test is used to test the hypothesis that an observed frequency (distribution) fits a given expected frequency distribution.

For example: observed control and experient proportion, 48% and 52%, fits 50% (expected).

Hypothesis testing:

H0: observed agrees with expected frequency (distribution)

H1: observed frequency does not fit with the expected frequency

Determine critical value: given degrees of freedom, alpha

Calculate Chi-square using the following formation:

If the calculated Chi-square is greater than the Cricial value, then the null hypothesis is rejected. The conclusion is that the observed frequency is different from the expected frequency.