The expression ‘necessary evil’ means that

  Undergraduate students in psychology and education come to their first course in statistics with diverse expectation of and background in mathematics. Some have considerable formal training and quantitative aptitude and look forward to learning statistics. Others – perhaps the majority, including some of those who aspire to postgraduate studies – are less confident in their quantitative skills. They regard a course in statistics as a necessary evil for the understanding or carrying out of research in their chosen fields, but an evil nonetheless.

  The third edition, like the predecessors, is directed primarily at the latter audience it was written with the conviction that statistical concepts can be described simply without loss of accuracy and that understanding statistical techniques as research tools can be effectively promoted by discussing them within the context of their application to concrete data rather than as pure abstraction. Further, its contents are limited to those statistical techniques that are widely used in the literature of psychology and to the principle underlying them.

  The changes that have been made in this edition reflect both the results of our teaching experience and the increasing prominence being given by statisticians to certain topics. Thus our discussion of some procedures, particularly those in the realm of descriptive statistics, which students grasp easily, have being shortened or rearranged. The treatment of other topics has been expanded. Greater emphasis has been placed on sampling theory, hypothesis testing, and the notion at statistical power.