Linear rational expectations models can have multiple equilibria, leading to sunspot equilibria where random factors affect the economy. This poses challenges for policy-making. A study on U.S. monetary policy found that the model used in previous research was limited, as it ignored the possibility of multiple equilibria. By extending estimation methods, researchers showed that sunspot shocks play a role in U.S. business cycles. They also developed a test to check if real data align with a unique equilibrium in the model.