Non-Parametric Analysis Methods

Abstract

As mentioned in Chapter 6, non-parametric tests are applicable in two circumstances: (1) when parametric tests cannot be used owing to the scale of the response variable, that is, the scale is nominal or ordinal, and (2) when, even when the scale of the response variable admits the use of parametric tests, that is, it is an interval or ratio scale, the observations gathered do not meet the constraints on normality called for by parametric tests. Remember that the methods of analysis that we discussed in earlier chapters (parametric methods) are subject to a series of constraints. Therefore, one of the steps taken in earlier chapters during the analysis process was to validate the mathematical model that explained the observations gathered from the experiment. An explanation of how to run these tests was given in these chapters. When these constraints are not met, the analysis of the data collected during experiments must switch to non-parametric methods.