A comparison helps explain a result only when the compared cases are relevant to the question. Careful anal identify impo similarities wh recognizing meani differences th could infl outcomes indepe of t particular fac under invest within each observed setting. Two classrooms may use different teaching materials but also differ in class size and prior experience. A difference in later performance cannot automatically be assigned to the materials alone. Considering alternative influences makes the conclusion more precise. The aim is not to find cases identical in every respect, but to understand which differences matter for the intended inference.

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