Income distribution is the other pillar of Kalecki's efforts to build a business cycle theory. To do this, Kalecki assumes that industries compete in imperfectly competitive markets, more particularly in oligopolistic markets where firms set a mark-up on their variable average costs (raw materials, wages of employees on the shop floor that are supposed to be variable) in order to cover their overhead costs (salaries to senior management and administration), to obtain a certain amount of profit. The mark-up fixed by firms is higher or lower depending on the degree of monopoly, or the ease with which firms can raise price without causing reduction in the quantity demanded.