Student's t-test is most frequently used to find out whether two groups of data are really different. The two groups can be independent (e.g., patients who were given a drug and patients who were given a placebo) or dependent (e.g., patients before and after treatments).

Student's t-test may apply to sample size as small as 10 or even smaller under certain conditions.

For independent samples, the sample size for the two groups don't have to be equal. The order of the data does not make any differences. For dependent (paired) samples, the samples must be paired (e.g., the before-treatment data must be paired with the after-treatment data for the same patient).

Online student's t-test calculator