Which statement summarizes the relationship between correlation and causation?

• A. Correlation proves causation.
• B. Causation and correlation are unrelated.
• C. Causation can be inferred from correlation alone.
• D. Causation requires evidence of a causal mechanism.

Answer: (D)

Correlation shows that two things move together, but it doesn’t explain why they move together. To claim that one thing causes the other, you need evidence that there is a plausible process linking the two, a mechanism that would explain how the cause leads to the effect. That causal mechanism helps rule out alternative explanations like a lurking third variable or coincidence, and it supports a directional, testable connection.

So the best statement is that causation requires evidence of a causal mechanism—without a mechanism, the observed relationship could be due to other factors or chance. The idea that correlation proves causation, or that correlation and causation are unrelated, or that causation can be inferred from correlation alone, are all misleading.