The null hypothesis usually refers to an assumption of what?

The null hypothesis is a fundamental concept in statistics, particularly in hypothesis testing. It typically posits that there is no effect, no difference, or no change in the population being studied. In other words, when researchers formulate a null hypothesis, they are asserting that any observed differences in their data are due to random chance rather than a true effect or relationship.

By assuming "no difference or no change," the null hypothesis provides a baseline against which the alternative hypothesis can be tested. This helps researchers determine whether their findings are statistically significant, as they will perform tests to evaluate the likelihood of observing their data if the null hypothesis were true.

In the context of the other options, claiming "some difference exists between groups" directly opposes the concept of the null hypothesis, as it aligns with the alternative hypothesis. "An increase in variance" does not pertain to the typical null hypothesis, which is more concerned with differences or changes regarding the means of populations. Lastly, while "random chance" is indeed a factor when discussing the null hypothesis, it is too vague and does not capture the specific assertion made by the null hypothesis concerning no effect or difference. Thus, the most accurate description of the null hypothesis is that it refers to the assumption of no difference or