What does it mean when experimental results show a significant difference at a p-value of 0.05?

What does it mean when experimental results show a significant difference at a p-value of 0.05?

• A. There is a 5% probability that the difference is real
• B. There is a 95% probability that the difference is real
• C. There were not enough animals in the experimental group to reach a conclusion
• D. The probability of finding a difference is 5%

Answer: (B)

The main idea is what a p-value tells you about chance when there is no real difference. A p-value of 0.05 means that if there were truly no difference between groups, you would expect to see a result as extreme as the one observed (or more) in about 5% of repeated experiments. Because this probability is so small, you reject the possibility that the observed difference is just due to random variation at the 5% significance level, and you infer there’s evidence of a real effect—often summarized as about 95% confidence that the difference reflects a real effect, assuming the study’s methods and assumptions are valid. This interpretation is about long-run frequency and evidence against chance, not a direct probability that the difference is real in this single study. The other statements either misstate what a p-value represents or bring in factors like sample size in a way that isn’t the direct meaning of the 0.05 result.

The main idea is what a p-value tells you about chance when there is no real difference. A p-value of 0.05 means that if there were truly no difference between groups, you would expect to see a result as extreme as the one observed (or more) in about 5% of repeated experiments. Because this probability is so small, you reject the possibility that the observed difference is just due to random variation at the 5% significance level, and you infer there’s evidence of a real effect—often summarized as about 95% confidence that the difference reflects a real effect, assuming the study’s methods and assumptions are valid. This interpretation is about long-run frequency and evidence against chance, not a direct probability that the difference is real in this single study. The other statements either misstate what a p-value represents or bring in factors like sample size in a way that isn’t the direct meaning of the 0.05 result.