In a one-sided test, it is stated before the analysis is carried out that it is only of interest if the location parameter is either larger than, or smaller than the given constant, whereas in a two-sided test, a difference in either direction is of interest.
A common situation is where the two populations correspond to research subjects who have been treated with two different treatments (one of them possibly being a control or placebo).
In this case, the goal is to assess whether one of the treatments typically yields a better response than the other.
The following tables provide guidance to the selection of the proper parametric or non-parametric statistical tests for a given data set.
The following table summarizes some common parametric and nonparametric tests for the location parameters of one or more samples.