What does alpha represent?

What does alpha represent?

• A. The probability of making a Type I error
• B. The threshold for the probability that a significant difference is due to chance
• C. The probability that a difference is real
• D. The power of the test

Answer: (A)

Alpha is the probability of making a Type I error in a hypothesis test—the chance of rejecting the null hypothesis when it is actually true. It is set in advance as the significance level (often 0.05) and acts as the threshold for declaring a result significant: if the p-value falls below alpha, you reject the null. So alpha represents the false positive rate you’re willing to accept. The idea described in the other choice is related to the decision rule, but the precise meaning is the risk of a false positive under the null. The remaining options refer to power or to the probability that a difference is real, which are different concepts.

Alpha is the probability of making a Type I error in a hypothesis test—the chance of rejecting the null hypothesis when it is actually true. It is set in advance as the significance level (often 0.05) and acts as the threshold for declaring a result significant: if the p-value falls below alpha, you reject the null. So alpha represents the false positive rate you’re willing to accept. The idea described in the other choice is related to the decision rule, but the precise meaning is the risk of a false positive under the null. The remaining options refer to power or to the probability that a difference is real, which are different concepts.