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 Is Reliability, and What Is an Example of How It Can be Established?

### What Is Reliability, and What Is an Example of How It Can be Established?

Reliability is the quality of an assessment tool such that its results are consistent, and it can take many different forms. Along with validity, reliability is one of two of the most important qualities of a test. If a test is not reliable, it cannot consistently assess a trait, characteristic, or level of performance, and its value as an assessment tool is questionable.

Understanding reliability includes knowing about the three components of any test score. These three components can best be understood by looking at the following equation:

$\text{Observed}\phantom{\rule{0.5em}{0ex}}\text{score}=\text{True}\phantom{\rule{0.5em}{0ex}}\text{score}+\text{Error}\phantom{\rule{0.5em}{0ex}}\text{score}$

The observed score is the score received on a test or an assessment tool, such as an 89 on a weekly science quiz or ...