Final answer:
Researchers create a theory when they develop a well-supported explanation for why people behave as they do, based on substantial data and experiments that verify hypotheses.
Step-by-step explanation:
When researchers collect enough data to develop an explanation of why people behave as they do, they are creating a theory. A theory is a well-supported explanation of observations that has been tested through experimentation and stands up to scrutiny. A theory emerges from hypotheses, which are testable educated guesses about predicted outcomes. Over time, if a hypothesis consistently explains a large body of experimental data, it may evolve into a theory, making theory the correct answer to your question.