If a researcher fails to reject the null hypothesis and the null hypothesis is not true has the researcher made a correct decision a Type I error or Type II error?

If a researcher fails to reject the null hypothesis when it is actually false, they have made a Type II error. This occurs when the researcher incorrectly concludes that there is not enough evidence to support an alternative hypothesis, despite it being true. In contrast, a Type I error happens when the null hypothesis is rejected when it is actually true.