T-Test

T-Tests are used to analyse skewed data or data with normal distribution

data with normal distribution

Compare paired vs unpaired data

Paired data occur when the individual observations of the first sample are matched to individual observations of the second sample. (same person).

Unpaired data occur when the observations of the first and second sample are independent of each other (different people)

3 types of t-test

What would you use an Independent Sample t-test for

What is a paired sample t test used for

What is a One Sample t-test used for

Use this procedure to test whether the mean of a single variable differs from a hypothesised value.

If the mean Birth weight of babies born in X Hospital is 3.5 kilos and the value that you would like to test is 4.0 kilos, use One sample t-test, to test if our sample data hospital X is different from the specified value

What types of data are required for the independent & dependent variables in a t-test

Independent: 1 nominal variable with 2 groups

Dependent: Scale

Degrees of Freedom

Number of observations in the data that are free to vary when estimating statistical parameters.

(Suppose you have 3 numbers: X, Y, Z and you know their mean = 10. You can pick any value for X​ and Y​. But once you pick X​ and Y​, Z​ is fixed because the total has to be 30. So only 2 numbers are free to vary. DF = 2)

Box Plot provides information about

the shape of the distribution

What do you call a t test where you assume equal variance

Pooled variance t test

What do you call a t test where you do not assume equal variance

Separate variance t test

When is Mann Whitney U used

when the assumptions of the independent sample t-test are not met.