Social Loss

Social loss is the social cost imposed by a monopoly.

Due to a lack of competition, a monopoly increases its profits by reducing its output and raising the price. Consumers suffer a social cost because there is less of the good available. An example is Microsoft Word. In a perfectly competitive market, the price of Microsoft word would be equal to its marginal cost (MC), which may be only $20. But instead Microsoft, by virtue of its near-monopoly, can sell it for perhaps $200. Fewer copies of Microsoft Word are available at that high price, and many computer users go without it.

It is a challenge to quantify the social cost of a monopoly. But it can be done as follows.

n a perfectly competitive market, each unit would have sold at its marginal cost (MC). But a monopoly can increase its profits by reducing its output and selling its good at a price greater than MC.

Consider the price P at the precise point when a particular unit goes from being sold to being unsold. When consumers were still willing to buy that unit, the overall value of that particular unit to society is P, because someone is willing to buy it for that price. Based on our assumption about this unit, when P for this unit is increased slightly, then no one buys it.

How much does society lose in value when the monopoly raises the price of that unit just high enough that no one buys it? Society would pay a price of MC for that good in a perfectly competitive market. But in that bargain society enjoyed a windfall value of (P-MC), because it was really willing to the higher price P for that same unit. When the good is withdrawn from the market, society loses the benefit of that extra value (P-MC) that it would have enjoyed in a perfectly competitive market. Thus the loss to society when a monopoly withdraws that particularly good is (P-MC).

The overall loss to society imposed by a monopoly is thus the sum of all the individual (P-MC) for each good withdrawn from the market. Because P is a function of output, the P is different for each unit withdrawn from the market as the monopoly raises its price.

Here is an example:

Question: Suppose Anthony owns a company having marginal costs of $5 for all his units. If he sells only one, then he reaps $11; selling two fetches a price of $10 piece; selling 3 attains a price of $9; selling four reaps $8; Q=5 would have P=$7; Q=6 has P=$6, Q=7 has P=$5, etc. A competitive firm would have the same cost and demand numbers. What does Anthony sell at, and what is the social cost of his monopoly?

Answer: If Anthony's company has monopoly and a marginal cost of $5 per widget, then using the described demand curve, his company should sell three widgets at $9 apiece or 4 widgets at $8 apiece. Either approach will give Anthony's company a profit of $12.

If Anthony sells only three widgets at $9, then that is four less than what a competitive market would sell. The social cost is the sum of (P-MC) over each of the withheld units, noting that the social cost for each withheld unit is different because the unit goes unsold at a different P.

We assume that society would have purchased the unit at slightly less than the higher price, such $6 minus an infinitesimal amount. When the price went from $5 to $6, one unit went unsold and the loss to society was almost (P-MC=$6-$5=$1). Likewise, another unit went unsold at $7 (P-MC=$2), another unit went unsold at $8 and another unit went unsold at $9. That total social cost is almost $1 + $2 + $3 + $4 = $10.

If instead Anthony sold 4 units at $8, then the social cost is almost $1 + $2 + $3 = $6. The "almost" is so close to the number that we drop the "almost" and simply provide the number as the estimated social cost.