What does Type II error indicate?

A Type II error occurs when the null hypothesis is not rejected, even though it is false. In other words, it indicates that a researcher has accepted the null hypothesis when there is, in fact, enough evidence to reject it. This error often relates to the failure to detect an effect or difference that truly exists, which can lead to incorrect conclusions about the effectiveness of a treatment or intervention.

This type of error is particularly relevant in studies where the power of the test—the probability of correctly rejecting a false null hypothesis—may be insufficient due to various factors such as a small sample size or inadequate effect sizes. A Type II error can result in missed opportunities for important findings that could advance knowledge in the field. Understanding this concept is critical for researchers, as it influences decisions about study design and the interpretation of results.