A randomized trial compares LDL cholesterol change on two diets, with alpha set at 0.05. The difference between groups has p = 0.03. Which interpretation is correct?
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Answer: A
Reject the null hypothesis; the difference is statistically significant: Correct. Because p (0.03) is below alpha (0.05), the null hypothesis of no difference is rejected and the result is statistically significant.
Fail to reject the null; the difference is not statistically significant: Wrong. A p-value below alpha leads to rejecting the null hypothesis.
There is a 97% probability that the new diet caused the LDL change: Wrong. A p-value is not the probability that the hypothesis is true. It is the probability of results this extreme if the null were true.
The result proves the difference is large enough to be clinically important: Wrong. Statistical significance says nothing about the size or clinical importance of the effect. Look at the effect size and confidence interval.
If p < alpha, reject H0 (statistically significant). Statistical significance is not the same as clinical significance. A Type I error is rejecting a true H0, and a Type II error is failing to reject a false H0.