Answer to Question 1
A forecast statement is a list of main points given towards the end of the introduction. It can be a bullet list on a visual or spoken by the presenter. It serves as roadmap for listeners to use throughout the presentation.
Answer to Question 2
Evidence must be adequateyour test sample must be big enough to be valid
Evidence must be representativeif your test sample is no good, the evidence is useless
Evidence must be plausiblethe link between cause and effect must be logical and reasonable. You must show that existence of one thing requires the existence of the other. If you find more than one possible cause, you must explain how you, as a professional, weighed the various factors to reach a conclusion