 Although the approach initially focused mainly on the rigidity of nominal prices, it was extended to wages and prices by Olivier Blanchard and Nobuhiro Kiyotaki in their influential article "Monopolistic Competition and the Effects of Aggregate Demand" .Huw Dixon and Claus Hansen showed that even if menu costs applied to a small sector of the economy, this would influence the rest of the economy and lead to prices in the rest of the economy becoming less responsive to changes in demand.While some studies suggested that menu costs are too small to have much of an aggregate impact, Laurence Ball and David Romer showed in 1990 that real rigidities could interact with nominal rigidities to create significant disequilibrium.