Equality of Proportions (chi squared test) Flashcards
What tests would you used to compare categorical/non-parametric data?
Chi squared tests
What test would you used to see whether the population proportion is equal to a certain value?
One sample χ2 test
What assumptions are needed for the one sample chi-square test?
▪️Observations are randomly and independently drawn
▪️Number of cells (categories) with expected frequencies less than 5 are less than 20%
▪️The minimum expected frequency is at the very least 1
What is the df for a one sample chi-square test?
categories-1
What test would you used to see whether the proportions in the population of one variable change based on another variable (are the proportions different) ?
Person’s chi square test
(Independent samples)
What is the null hypothesis of a person’s chi square test?
There is no association between the two variable (proportions are the same)
What assumptions are needed for Pearson’s chi square test?
▪️Observations are randomly and independently drawn
▪️Number of cells with expected frequencies less than 5 are less than 20%
▪️Minimum expected frequency is at the very least 1
▪️Observations are not paired
When do you check assumptions for chi-square tests?
AFTER the test
Look at bottom of the table
How do you know whether to compare proportions by row or column for a Pearson’s chi square test?
You cannot statistically compare proportions that add up to 100%
If they add by column, compare them by row!
We cannot compare proportions that….
Add up to 100%!!
Why can’t you compare proportions that add up to 100?
▪️Only the descriptive indices of one of the variables
▪️Doesn’t consider the relationship between variables
E.g. 15 of the 30 who died were vaccinated. Reporting it as 50% is just descriptive of those who died, it doesn’t consider the rest of the population who didnt
What is the df for a Pearson’s chi square test?
(c1-1)(c2-1)
For a 2x2 grid this is 1
What test do we use to see whether the proportion of a variable changes based on another matched variable (is proportion in one condition different to that in the same/paired group in another condition?
McNemar χ2 test
What is the null hypothesis of a McNemar chi square test?
There is no association between two (paired) variables
What assumptions are needed for the McNemar chi square test?
▪️Observations are randomly and independently drawn
▪️At least 25 observations in the discordant cells
▪️Data are paired
