Most researchers create their thesis statement by intuition - based on what they are doing. They are usually more or less right but that is not the best way of doing things.
The correct way to create the thesis statement is to collate the aggregate of the dependent variables and the aggregate of the independent variables. This ensures that the research questions generated lead to the hypothesis which lead to the findings.
If the Findings confirm the Claims then the Thesis Statement, in retrospect, must hold.