Consumer and producer surplus — common mistakes

When drawing diagrams for price controls, always clearly label the original and new surplus areas. The deadweight loss triangle points towards the equilibrium point and its base is the vertical line at the new, lower quantity traded. Be prepared to calculate the value of these areas if given numerical data.

For a single, voluntary transaction, no. A rational consumer will not purchase a good if the price is higher than their willingness to pay. However, if a consumer misjudges their utility or is forced to buy, it's theoretically possible. In aggregate market analysis, consumer surplus is always considered as a non-negative value, representing the total benefit to all consumers who do purchase the good.

This is a common point of confusion. A price ceiling creates a shortage (quantity demanded exceeds quantity supplied). The consumers who are still able to buy the good benefit from the lower price, increasing their individual surplus. However, many other consumers are now unable to buy the good at all and lose their entire potential surplus. If this loss of surplus from consumers being pushed out of the market is greater than the gain for those who still buy, the total consumer surplus can decrease.

Not exactly, although they are closely related. Producer surplus is the total revenue minus the total variable costs (as the supply curve represents marginal cost). Profit, on the other hand, is total revenue minus total costs (both variable and fixed). In the short run, where fixed costs exist, profit will be lower than producer surplus. A firm's primary goal is to maximise profit, not producer surplus, but actions that increase producer surplus often lead to higher profits.