Which statement about Type I and Type II errors is correct?

Which statement about Type I and Type II errors is correct?

• A. Type I error occurs when you fail to reject a true null.
• B. Type II error occurs when you reject a false null.
• C. Type I error is a false positive; Type II error is a false negative.
• D. Type I error is about external validity; Type II about internal validity.

Answer: (C)

In hypothesis testing, two error types describe what can go wrong when we make a decision about the null hypothesis. A Type I error occurs when you reject a true null hypothesis—this is a false positive. A Type II error occurs when you fail to reject a false null hypothesis—this is a false negative. This statement is best because it pins down the exact meanings of the two errors. For example, if the null hypothesis is that a treatment has no effect, rejecting it when there really is no effect would be a Type I error; failing to reject it when there actually is an effect would be a Type II error. The other options mix up the definitions—one describes a mischaracterization of the error, and another confuses error types with study validity rather than the decision about the null.

In hypothesis testing, two error types describe what can go wrong when we make a decision about the null hypothesis. A Type I error occurs when you reject a true null hypothesis—this is a false positive. A Type II error occurs when you fail to reject a false null hypothesis—this is a false negative. This statement is best because it pins down the exact meanings of the two errors.

For example, if the null hypothesis is that a treatment has no effect, rejecting it when there really is no effect would be a Type I error; failing to reject it when there actually is an effect would be a Type II error. The other options mix up the definitions—one describes a mischaracterization of the error, and another confuses error types with study validity rather than the decision about the null.