That statement is a hypothesis. Hypothesis is related to hypothetical. A hypothesis is a statement of what your study results might be. The hypothesis will be tested using inferential statistics. Based on the outcome of those inferential statistics, you will decide whether your hypothesis is consistent with the data you collected.
Some people suggest the primary activity of science is hypothesis testing.
In stating the hypothesis, the variables of interest need to be clearly defined. The variables should be operationally defined. For example, if you are studying aggression, you might define aggression as the number of times your subjects bop each other on the head. An important thing to notice here is that operational definitions do not mean that the thing being defined is equal to what it is being defined as. That is, head bops are not equal to aggression.