Which of the following is an example of a Type I error?

A Type I error occurs when a true null hypothesis is incorrectly rejected. In the context of the question, rejecting a drug's effectiveness when it is actually effective is a classic example of a Type I error. This means that the statistical test concludes that the drug does not work when, in reality, it does, leading to a potentially harmful decision to not use an effective treatment.

This scenario highlights the consequence of being overly cautious or misinterpreting data, which can result in overlooking beneficial options. Recognizing the implications of Type I errors is critical in research and clinical decision-making, as it can affect the approval of treatments and influence public health outcomes.