What is a Type II error in statistical testing?

A Type II error, also known as a beta error, occurs when a researcher fails to reject a false null hypothesis. In statistical hypothesis testing, the null hypothesis typically represents a statement of no effect or no difference. When the null hypothesis is actually false but the test fails to reject it, this indicates that the study did not detect a true effect or relationship that exists.

This error is particularly concerning because it implies that researchers might conclude there is no significant effect when, in reality, one does exist, potentially leading to mistaken decisions or conclusions based on the data. Understanding a Type II error is crucial for researchers designing experiments because it highlights the importance of having adequate power and sample size to increase the likelihood of detecting true effects.