The study looked at different economic models in small open economies to see if the rules that work in closed economies also work in open ones. They found that the rules that work in closed economies don't always work in open ones because of differences in interest rate smoothing. A first difference rule can help stabilize open economies, but it doesn't work well in all models. This means that choosing the wrong model in open economies can have serious consequences, so policymakers need to understand the true structure of these economies to make good decisions.