Final answer:
A Type I error occurs when we do not reject the null hypothesis when it is actually false.
Step-by-step explanation:
A Type I error occurs when we do not reject the null hypothesis when it is actually false.
For example, let's say a researcher is testing whether a new drug is effective in treating a certain disease. The null hypothesis is that the drug has no effect, while the alternative hypothesis is that the drug is effective. If the researcher fails to reject the null hypothesis (i.e., concludes that the drug has no effect) when in reality it does, then a Type I error has occurred.