Which one of the following statements is incorrect? We use different macroeconomic models for economic analysis because the economy behaves differently depending on how much time has passed after a demand shock. The differences in economic behavior result from the fact that prices go from completely stuck immediately after a shock to completely flexible in the long run. Using the same model to study the different stages in a demand shock process gives us much better insight than using different models for the short run and long run. By using different economic models, we learn how various government and central bank policies may have different effects in the short run (when prices are fixed) versus the long run (when prices are flexible)