Perfect Competition Review for AP Economics (page 3)
Review questions for this study guide can be found at:
Main Topics: Structural Characteristics, Demand, Profit Maximization, Short-Run Profits, Decision to Shut Down, Long-Run Adjustment
Structural Characteristics of Perfect Competition
Each market structure is defined by structural characteristics. These characteristics determine, among other things, how the profit maximizing price and quantity are set in the short run, as well as how profits might be maintained in the long run. Perfect competition is typically described by four characteristics:
- Many small independent producers and consumers. Not small like Mini-Me small, but small like each firm is too small to have an impact on market price. No one firm can drive up the price by restricting supply, or drive down the price by flooding the market with output. No one consumer can, by changing the amount of the good that he consumes, impact the price.
- Firms produce a standardized product. There exist no real differences between one firm's output and the next.
- No barriers to entry or exit. There exist no significant obstacles to the entry of new firms into, or the exit of existing firms out of this industry. Profitability or lack thereof determines whether the industry is expanding or contracting.
- Firms are "price takers." This characteristic is actually a result of the first three. Because all firms are too small to affect the price, they must accept the market price and produce as much as they wish at that price. Even if they couldchange the price, they would not do so. To see this, suppose that the market determined competitive price of barley is $5. If farmer Katie increased the price to $5.01, she would now be the high price supplier of barley with thousands of competitors producing an identical product at a lower price; Katie is likely to lose all of her customers. If she lowers her price to $4.99, she would seemingly clean up her competition. But remember, the price-taking characteristic tells us that Katie can sell all she wants at the market price of $5. If you can sell all you want at $5, why would Katie sell even one unit at $4.99?
All four of the characteristics of perfect competition are rarely found in today's industries, but agricultural commodities are usually regarded as approximately perfectly competitive.
Demand for the Firm
Each perfectly competitive firm produces a standardized, or homogenous, product. Because each firm's output is such a small share of the total market supply, the demand for each firm's output is perfectly elastic. Perfectly competitive firms have no effect on the market price; they simply produce as much as they can at the going price. This implies a horizontal demand curve for their product. This does NOT imply that the market demand curve is horizontal. If the market price of barley falls, quantity demanded rises. Figure 9.1 illustrates the difference between market demand (D) and the demand for one firm's product (d).
Let's get one thing straight. When we say firms maximizeeconomic profit, this means they are not going to settle for anything less than the highest possible difference between total revenue and total economic cost. If an additional dollar of profit is to be earned, they take that opportunity. If the maximum profit possible is actually zero, or even negative dollars, they accept this short-run outcome. There are two equivalent ways to maximize economic profit.
The Method of "Totals''
The perfectly competitive firm cannot change the price; it can only adjust output. To maximize profit the firm selects the output to maximize:
Economic Profit (π) = Total Revenue – Total Economic Cost
An example should help to illustrate how a firm goes about maximizing profit.
A carrot farmer operates in a perfectly competitive market. The going price for a bushel of carrots is $11. Table 9.1 summarizes how total revenue, total cost, and profit differ at various levels of output. Because it is the short run, there exist $16 of fixed costs. All costs reflect the explicit and implicit costs of hiring a resource.
Because the firm is a price taker, the level of output does not affect the going price. Total costs rise as production increases, a concept seen in the previous chapter. As a profit maximizer, our carrot farmer would choose to produce five bushels per day and earn $2 in daily economic profit. This method of profit maximization is much like "trial and error" and is a bit cumbersome. Let's explore an equivalent, and easier way.
The Method of "Marginals"
Throughout this book we have seen illustrations of marginal analysis and this situation is no different. You'll recall that rational decision making implies:
Since the only decision to be made by the perfectly competitive firm is to choose the optimal level of output, the firm's rule is:
- Choose the level of output where MR = MC.
Table 9.2 can be modified to show the marginal revenue and marginal cost of selling additional bushels of carrots.
Notice that in perfect competition, the price is equal to marginal revenue. This is fairly simple if you recall the assumptions of the model. Farmers can sell as much as they want at the market price. If a farmer sells one more bushel, total revenue increases by the price of the bushel; $11 in this case. Sell another bushel; earn another marginal revenue of $11. Price is also equivalent to average revenue (AR), or total revenue per unit. These relationships can be seen in Figure 9.2
- MR = ΔTR/ΔQ= P × ΔQ/ΔQ= P
- AR = TR/Q= P × Q/Q= P
- P = MR = AR = demand for the firm's product
Short-Run Profit and Loss
To maximize profit, the firm must choose the level of output (qe) where MR = MC. But how can we use Figure 9.2 to identify these profits? A little algebra goes a long way.
Π = TR – TC = P × qe – TC. If you divide both terms by quantity and remember that TC/q= Average Total Cost, you have:
Π = qe × (P– ATC)
The term (P– ATC) is the per unit difference between what the firm receives from the sale of each unit and the average cost of producing it, or profit per unit. When you multiply this per unit profit by the number of units (qe) produced, you have total profit. Table 9.3 and Figure 9.3 incorporate the ATC into our carrot farmer's table profit maximizing decision.
Profit Rectangles and Flying Monkeys
Everyone remembers The Wizard of Ozand the critical instructions that the people of Munchkinland gave Dorothy and Toto as they set off to find the Wizard: "Follow the yellow brick road." And when Dorothy, Toto, and friends stayed on the yellow brick road, they were fine. Whenever they ignored these cautionary words and left the yellow brick road, bad things happened—the scariest being the arrival of the flying monkeys. The flying monkeys tore the Scarecrow limb from limb and set the Scarecrow's straw innards on fire. Talk about a Rolaids moment! Very bad things happen when you leave the yellow brick road.
When you find the profit maximizing level of production, qe, you are locating the yellow brick road for this firm. Neverleave this level of output, or bad things happen. Finding qe is the first step in calculating profit with a "profit rectangle." The area of the shaded rectangle is 5 bushels wide, multiplied by 40 cents high. In our case, the price $11 is in Figure 9.3 above the average total cost $10.60 so we have positive economic profits of $2. This does not always occur in the short run. Another look at our per unit equation tells us:
While firms would love to maintain the above scenario where P> ATC and positive economic profits are made, it might not always turn out that way. Due to a failure of the Bugs Bunny diet fad, the market for carrots suffers a dramatic decrease in demand. Plummeting demand decreases the market price to $6.50 per bushel and firms must readjust their profit maximizing output decision.
At the much lower price of $6.50, the firm now finds that MR = MC at an output of three bushels per day. Not surprisingly, the opportunity for positive economic profit has been eliminated. The profit maximizing, or loss minimizing, output of three bushels provides the best possible scenario for the firm; but that scenario involves economic losses of $14.50. The rectangle can still be seen in Figure 9.4, where average total cost is $11.33 per bushel.
- Many AP students lose points because they incorrectly locate and label profit. When finding the profit/loss rectangle, it is important to remember the following.
Decision to Shut Down
Firms obviously do not enjoy producing at a loss and desperately hope that the market price improves so that profits are possible. However, if firms are incurring losses, they must decide whether it is economically rational to operate at all. The decision to shut down, or produce zero, in the short run is sometimes the optimal strategy. To see why, consider what happens when a firm begins to produce. When a perfectly competitive firm decides to produce any level of output greater than zero, two things happen.
- It collects total revenue (TR) = P × qe, and
- It incurs variable costs (TVC). Of course the firm also incurs total fixed costs, but it incurs those costs anyway, regardless of the level of output.
If the firm, by producing in the short run, can collect total revenues that at least exceed the total variable costs, then it continues to produce, even at a loss. However, if producing output incurs more variable cost than revenue collected, why bother? Shut down, hope for better times, and suffer losses equal to TFC. This comparison provides us a decision rule for shutting down in the short run.
- If TR ≥ TVC, the firm produces qe where MR = MC.
- If TR < TVC, the firm shuts down and q = 0.
The Shutdown Point
We can see the shutdown point in Figure 9.5 by converting the above decision rule into a per unit comparison. Dividing total revenue and total variable cost by qtells us to shut down if P< AVC. This is the identical decision rule; it is just a per unit comparison of revenue and variable cost.
- If P ≥ AVC, the firm produces qe where MR = MC.
- If P< AVC, the firm shuts down and q = 0.
In Figure 9.5, there are four prices shown.
- PH is the highest price. At qh, the firm earns enough total revenue to cover all costs. Π > 0.
- PM is the middle price. At qm, the firm's TR exceeds TVC but only covers part of the TFC. Π < 0.
- PD is the shutdown price. At qd, the firm's TR just covers TVC and the firm is at the shutdown point. If price falls any lower, the firm does not produce.
- PL is the lowest price. At q1, the firm's TR cannot even cover TVC and so the firm shuts down, producing q= 0. Π = –TFC.
As you can see in Figure 9.5, when the price fluctuates between PH and PD, the firm finds a new profit maximizing quantity where P = MR = MC. If price increases, quantity supplied increases. If price decreases, quantity supplied decreases. This is a restatement of the Law of Supply. This movement upward and downward along the marginal cost curve implies that MC serves as the supply curve for the perfectly competitive firm. The only exception is when the price falls below the shutdown point (minimum of AVC) and the firm quickly decides to produce nothing. The market supply curve is simply the summation of all firms' MC curves.
- The MC curve above the shutdown point serves as the supply curve for each perfectly competitive firm.
- The market supply curve is therefore the sum of all of the MC curves. S = Σ MC.
The short run is a period of time too brief for firms to change the size of their plants. This means that it is also too short for existing firms to exit the industry in bad times and too short for new entrepreneurs to enter the industry in good times. The "free entry and exit" characteristic of perfect competition assures us that in the long run, we can expect to see firms either exiting or entering, depending upon whether profits or losses are being made in the short run. We'll first examine the case where short-run positive profits are made in the carrot industry and then the situation where short-run losses are incurred.
- In virtually all of the past AP Microeconomics exams, free-response questions have appeared that test the students' knowledge of perfect competition and the difference between the short- and long-run equilibria.
Short-Run Positive Profits
Figure 9.6 illustrates the perfectly competitive carrot industry where the market price is above average total cost. Firms are earning positive short-run profits, as illustrated by the shaded rectangle.
So what next? Well many entrepreneurs on the outside of this market are attracted by the positive short-run profits being made by carrot producers. Given sufficient time (i.e., the long run), these new firms enter the market. With more carrot producers, the market supply curve shifts outward, driving down the price. As the price falls, the profit rectangle gets smaller and smaller until it actually disappears. At the point where P= MR = MC = ATC each carrot farmer is now breaking even with Π = 0. Would the next potential carrot farmer enter the market? Unlikely, as the entry of one more firm pushes the price down just enough to where losses are actually incurred. Thus this break-even point is described as the long-run equilibrium. The market quantity has increased and each firm produces less at the lower price. Figure 9.7 illustrates the movement toward the long-run equilibrium.
The long-run adjustment to short-run positive profits can be summarized as:
What's So Great About Breaking Even?
Remember there is a distinction between accounting profit and economic profit. Economic profit subtracts the next best opportunity costs of your resources from total revenue. If you are still breaking even after subtracting what you might have earned in all of those other opportunities, you can't feel cheated. In other words, you are making a fair rate of return on your invested resources and you have no incentive to take them elsewhere. Sure, you would like to earn more than zero economic profit (a.k.a. "normal profit") but the characteristics of perfect competition rule this out.
Figure 9.8 illustrates short-run losses with a price below ATC but above the shutdown point. The long-run adjustment story might sound familiar, only with market forces moving in the opposite direction.
Again, we should ask "What next?" Some existing firms in this market begin to exit the industry. With fewer carrot producers, the market supply curve shifts inward, driving up the price. As the price rises, the loss rectangle gets smaller and smaller until again it disappears. At the point where PLR = MR = MC = ATC each remaining carrot farmer is now breaking even with Π = 0. Would another carrot farmer exit the market? Possibly, but the exit of one more firm bumps up the price just enough so that a small positive profit is earned, prompting one firm to enter and get us back to the break-even point. Arrival at the break-even point is once again the long-run equilibrium. The market quantity has decreased, but each surviving firm produces more at the higher price. Figure 9.9 illustrates the movement toward the long-run equilibrium.
The long-run adjustment to short-run losses can be summarized as:
Summarizing in Table 9.5, there are four possible short-run scenarios and resulting long-run adjustments to the perfectly competitive equilibrium, which always ends in the same place.
Are There Variations on This Story and Do I Need to Know Them?
Yes and maybe. Throughout this section we have made an assumption that entry and exit of firms has no impact on the cost curves of firms in the market. In other words, we have been assuming a constant cost industry. Recent AP Microeconomics exams have made references to constant cost industries and (maybe) caused unnecessary confusion for test takers. It is always possible that future exams will refer to constant, increasing or decreasing cost industries so you should probably become familiar with these terms. A quick explanation and you will not be one of the confused.
Suppose that entry of new firms into a profitable carrot market increases the demand for key resources like land, labor, and capital. Increased demand for these resources might increase the cost of employing those resources. When this happens, the cost curves for firms in the carrot industry start to shift upward. This situation is described as an increasing cost industry. Graphing this situation gets sticky, but if you follow the logic you will be fine. The entry of new firms drives down the price of the output andincreases the cost curves so the profit is eliminated more quickly than with our constant cost industry. Fewer firms eventually enter this version of the carrot market and the new long-run price is higher than it is in a constant cost industry.
A decreasing cost industry is one in which the entry of new firms actually decreases the price of key inputs and causes the cost curves to shift downward. This might occur because producers of the key inputs expand production and experience economies of scale and lower per-unit costs. Since the entry of new firms lowers the price of the output and decreases the cost curves, it takes longer for the profit to be eliminated than in our constant cost industry. More firms can eventually enter this market and the new long-run price is lower than it would be in a constant cost industry.
Review questions for this study guide can be found at:
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