In an increasingly data-driven world, it is more important than ever for students as well as professionals to better understand basic statistical concepts. 100 Questions (and Answers) About Statistics addresses the essential questions that students ask about statistics in a concise and accessible way. It is perfect for instructors, students, and practitioners as a supplement to more comprehensive materials, or as a desk reference with quick answers to the most frequently asked questions.

What Are a Type I and a Type II Error?

What Are a Type I and a Type II Error?

A Type I error (also called significance level or alpha, represented by the Greek letter α) is the probability of rejecting a null hypothesis when it is indeed true. A goal of our work is to minimize that error. Remember that since the null hypothesis is based on the population, which is never directly tested, we never really know whether the null is true or false.

For example, let’s say that we are reasonably confident that there is a difference between males and females in their verbal SAT scores. The null state reflected by the hypothesis is that there is no difference between the two groups. We test the research hypothesis that there is a ...