The null hypothesis is best described as?

• A. There is no effect or difference; any observed differences are due to chance
• B. There is a real effect
• C. The results prove the treatment works
• D. The alternative hypothesis is true

Answer: (A)

In hypothesis testing, the null hypothesis is a starting statement that there is no effect or difference between groups or conditions; any observed differences are just due to random variation. This sets a baseline model for what we would expect if nothing real is happening. We then see whether the data provide strong evidence against that baseline. If they do, we reject the null and consider that there may be a real effect. But we do not claim absolute proof of the effect; we’re making a probabilistic judgment based on the data.

This is why the statement about no effect being the best description fits: it captures the idea that anything observed beyond what would be expected by chance is what researchers test against the null. The other ideas describe the alternative hypothesis (there is a real effect), claim proof of a treatment’s effectiveness (statistics don’t provide absolute proof), or assert the truth of the alternative hypothesis (we can’t declare that with certainty from data).