Fiona wants to test her prediction, also known as a that "lack of sleep increases the likelihood of lower test scores for college students."

The answer is hypothesis.

Explanation:

A hypothesis is a possible explanation for a phenomenon. To be regarded as scientific, a hypothesis should be able to be tested.

Although often used interchangeably, a hypothesis is different from a theory. While the former is an educated assumption that can be researched in the future, the latter is a confirmed explanation with scientific basis.