A researcher is interested in whether high school students who play sports have a higher or lower body mass index than students in the general population

A hypothesis can be that, There is a significant difference between high school students who play sport and those who don't in their body weight index.

A hypothesis is a supposition made by the scientist. In order for a hypothesis to be a scientific hypothesis, the scientific method requires for it to be tested. If a hypothesis cannot be tested, it cannot be scientific hypothesis. It is important to state the hypothesis clearly at the beginning of a scientific paper. This enables the reader to understand the problem.