Understanding P-value of 0.05 in Clinical Trials
The correct answer is B: The probability is 1 in 20 that the observed differences could have happened by chance alone.
What P = 0.05 Actually Means
A P-value of 0.05 indicates that if there were truly no difference between the drug and control groups (the null hypothesis), there would be only a 5% probability (1 in 20 chance) of observing a difference as large as or larger than what was actually found, purely by random chance 1.
Why the Other Options Are Incorrect
Option A is wrong because P = 0.05 provides no information about the magnitude of effect (such as "20 times less likely"). The P-value only addresses statistical significance, not the size of the treatment benefit. The actual risk reduction would need to be calculated from relative risk or hazard ratios reported separately in the study 1.
Option C is incorrect because the P-value does not predict reproducibility of results in future trials. While P = 0.05 suggests statistical significance in this particular trial, it does not guarantee that repeating the study would yield the same findings. Reproducibility depends on multiple factors including sample size, population characteristics, and study design 1.
Option D misinterprets the statistic by suggesting it applies to individual patient outcomes (19 of 20 patients). The P-value is a population-level statistical measure about the likelihood of the observed group difference occurring by chance, not a statement about individual patient response rates 1.
Option E is unrelated to the P-value, as it would describe the actual mortality rate in the study population, which is a separate descriptive statistic entirely independent of the P-value calculation 1.
Clinical Context for Hepatitis Treatment
In chronic hepatitis trials, demonstrating reduced case fatality with P = 0.05 represents meaningful evidence of treatment benefit. Studies have shown that achieving sustained virologic response (SVR) in hepatitis C is associated with substantial mortality reduction (RR = 0.45; 95% CI = 0.41–0.51), though confidence in such estimates requires careful consideration of study design and potential confounders 1. For hepatitis B, long-term viral suppression with antiviral therapy has been associated with regression of liver fibrosis and reduced hepatocellular carcinoma risk in cohort studies, though cure rates remain low (3-7% with pegylated interferon, 1-12% with nucleos(t)ide analogues) 2.
Important Caveats
The P = 0.05 threshold is arbitrary and represents a conventional cutoff rather than a definitive boundary between "significant" and "non-significant" results. A result with P = 0.05 still means there is a 5% chance the observed difference occurred by random variation alone, which is not negligible 1. Additionally, statistical significance does not automatically translate to clinical significance—the actual magnitude of benefit and its relevance to patient outcomes must be evaluated separately 1.