The article compares two different models to predict economic output in Japan, the UK, and the US from 1960 to 1990. The demand-side model is better at forecasting total output, while the supply-side model is more accurate for specific sectors like agriculture and mining. However, the construction sector's performance is predicted better by the demand-side model in Japan, but by the supply-side model in the UK and US. Both models are important for understanding whether an economy or sector is driven by demand or supply.