T-test (paired and unpaired)

• 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
  • applied to two independent groups e.g. diabetic patients versus non-diabetics
  • sample size from the two groups may or may not be equal
  • in addition to the assumption that the data is from a normal distribution, there is also the assumption that the standard deviation (SD)s is approximately the same in both groups

• 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

Reference:

1. Doctor (March 22nd 2005):33-35.