The study looked at how the U.S. made trade policies during the Smoot-Hawley tariff in 1930. They used a model to see how tariffs were decided based on import demand, export supply, and lobbying by workers and firms. By analyzing data from 1927-35, they found that most tariffs were influenced by firm lobbies, but some were based on trade terms. In 1931, workers pushed for more protection in the Smoot-Hawley tariff.