What is a Type I error?

A Type I error occurs when a researcher incorrectly rejects a true null hypothesis. In hypothesis testing, the null hypothesis represents a statement of no effect or no difference, and rejecting it implies that there is an effect or a difference when, in reality, there isn’t one. This type of error is significant because it can lead to false conclusions in a study, suggesting that a treatment or an intervention is effective when it is not.

The significance level, often denoted by alpha (α), is the threshold used to determine whether to reject the null hypothesis. A common significance level is 0.05, indicating a 5% probability of making a Type I error. Hence, the recognition of a Type I error is crucial in research as it emphasizes the importance of controlling this risk in hypothesis testing to ensure valid outcomes.