The study looked at different theories about how companies decide to invest money in new projects. By analyzing data from US manufacturing firms, they found that the neoclassical model was the best in time-series regressions, while the cash flow model was the top choice in cross-section and fixed effects regressions. This means that cash flow is the most important factor influencing a company's decision to spend money on new investments. These results support the idea that a mix of theories is needed to understand how companies make investment decisions, and show that looking at individual companies is crucial for this type of research.