Scope of inference has two doors. Random selection answers “Who can we speak about?”… it buys you generalization to the larger population. Random assignment answers “Why did it happen?”… it buys you causal language inside your study. Different keys, different locks. If you have neither, be humble. If you have one, say which door it opens. If you have both, celebrate… but still check your hinges (measurement and execution). The fastest way to get in trouble is to grab the wrong key and declare victory. Before writing a conclusion, underline the sentence that states what you can infer… and what you can’t.
