p-value is the actual probability that the observed difference occurred by chance alone. Which choice best describes this statement?

p-value is the actual probability that the observed difference occurred by chance alone. Which choice best describes this statement?

• A. The probability that the null hypothesis is true
• B. The probability that the observed difference occurred by chance alone
• C. The probability of a Type I error
• D. The probability of replicating the result

Answer: (B)

A p-value measures how compatible your data are with the assumption that there is no real effect. Specifically, it is the probability, under the null hypothesis, of obtaining a result as extreme as the one observed (or more extreme) purely due to random sampling variation. Saying the p-value is the probability that the observed difference occurred by chance alone aligns with this idea: the observed difference could arise from random fluctuations if there is no true effect. It is not the probability that the null hypothesis is true, not the probability of making a Type I error, and not the probability that the result would be replicated in another study.

A p-value measures how compatible your data are with the assumption that there is no real effect. Specifically, it is the probability, under the null hypothesis, of obtaining a result as extreme as the one observed (or more extreme) purely due to random sampling variation. Saying the p-value is the probability that the observed difference occurred by chance alone aligns with this idea: the observed difference could arise from random fluctuations if there is no true effect. It is not the probability that the null hypothesis is true, not the probability of making a Type I error, and not the probability that the result would be replicated in another study.