What is a paired and unpaired t-test? What are the differences?

Unpaired t-test (also known as the student’s t-test) and the paired t-test both assume that analysed data is from a normal distribution.

Unpaired t-test

  • It is applied to two independent groups e.g. diabetic patients versus non-diabetics.
  • Sample size from the two groups may or may not be equal
  • T-test compares the means of the two groups of data – the test determines whether the data has come from the same population or not. The mean difference is calculated (this can be a positive or negative value); also a 95% confidence interval for the mean difference is calculated. A p-value is calculated where p is the probability of a false-positive event. An example relating to data regarding patients with diabetes in chronic heart failure.

Paired t-test

  • Data is derived from study subjects who have been measured at two time points (so each individual has two measurements). The two measurements generally are before and after a treatment intervention
  • 95% confidence interval is derived from the difference between the two sets of paired observations.

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