The article discusses how competition in markets is often measured by substitutability between products. However, the researchers argue that this approach can mix up the price effect of competition with a pure allocation effect. They show that higher substitutability leads to resources shifting towards more productive sectors, while changes in market structure (like monopolistic competition versus Bertrand duopoly) do not affect the relative prices of goods if markups are symmetric. This means that changes in competition may not always have a direct impact on prices in the market.