In hypothesis testing, which value indicates the probability of observing the data under the null hypothesis?

• A. Alpha value
• B. Degrees of freedom
• C. Test statistic
• D. P value

Answer: (D)

The P value is the probability, under the null hypothesis, of obtaining results as extreme as what was observed (or more extreme). It tells you how compatible your data are with H0. If that probability is very small, the data don’t fit well with the null, which is why researchers compare the P value to a pre-set significance level to decide whether to reject H0.

The other terms play different roles: the alpha value is the threshold you set for declaring significance, not the probability of the observed data. Degrees of freedom shape the reference distribution but aren’t a direct probability about the observed outcome. The test statistic is the calculated measure from your data used to compute the P value or compare to a critical value, but by itself it isn’t the probability of observing the data under the null.