Gay, Mills, & Airasian (2009). Educational research: Competencies for analysis and applications (9th edition).


“Nonparametric tests are not as powerful as parametric tests. In other words, it is more difficult with a nonparametric test to reject a null hypothesis at a given level of significance; usually, a larger sample size is needed to reach the same level of significance as in a parametric test.” (p 335)

See this page at

Morgan, Leech, Gloeckner, & Barrett (2013). Measurement and Descriptive Statistics (Chapter 3).


“We believe that the terms nominal, dichotomous, ordinal, and approximately normal (for normally distributed) are usually more useful that the traditional or SPSS measurement terms for the selection and interpretation of statistics.” (p 39)

See this page at