【A Level經濟】微觀經濟你一定要知道的10張圖！！

02-20

Diagrams Check

考試中大家對圖表又愛又恨：它是很關鍵的得分點，但是有些同學對圖表不夠熟悉在畫圖上浪費了很多時間，那微觀經濟中比較關鍵的圖表都有哪些呢？

1. The law of diminishing returns

In the short run, the law of diminishing returns state that as we add more units of a variable input(i.e.labour or raw materials) to fixed amounts of land and capital, the change in the output will at first rise then fall.

我們也可以從Marginal Product的角度來想，比如我們假設其他變數不變然後增加Labour的數量，剛開始MP會增加，但後來員工越來越多造成擁擠，MP會慢慢地下降，Total output會上升但是斜率在慢慢下降。

2. Fixed and Variable Costs in the short run

關於FC和VC的要點：

1. Fixed costs are independent of output and must be paid out even if the production stops.

2. Capital-intensive industries with a high ratio of fixed to variable costs offer scope for economies of scale.

3. AFC=Fixed Costs(FC)/Output(Q).

4. Marginal costs(MC) cuts both AVC and ATC at the minimum point of each.(Draw accurately!)

3. Economies of scale/Diseconomies of scale

這裡大家需要知道的還包括diseconomies of scale的原因：

1. Control – monitoring the productivity and the quality of output from thousands of employees in big, complex corporations is imperfect and expensive–this links to the concept of the principal-agent problem i.e. the difficulties of shareholders monitoring the performance of managers.

2. Co-ordination - it can be difficult to co-ordinate complicated production processes across several plants in different locations and countries. Achieving efficient flows of information in large businesses is expensive as is the cost of managing supply contracts with hundreds of suppliers at different points of an industry』s supply chain.

3. Co-operation - workers in large firms may develop a sense of alienation and loss of morale. If they do not consider themselves to be an integral part of the business, their productivity may fall leading to wastage of factor inputs and higher costs

4. Natural Monopoly and Economic Efficiency

A natural monopoly occurs in an industry where LRAC falls over a wide range of output levels such that there may be room only for one supplier to fully exploit all of the internal economies of scale, reach the minimum efficient scale and therefore achieve productive efficiency.

The major utilities such as gas, electricity and water are often put forward as examples of industries with strong "natural tendencies" towards being a natural monopoly in part because of the huge fixed costs of building and maintaining nationwide networks / infrastructures of cables and pipes.

Key Point: A natural monopoly is characterised by increasing returns to scale at all levels of output – thus the long run cost per unit (LRAC) will drift lower as production expands. LRAC is falling because long run marginal cost is below LRAC.

5. Average, marginal and total revenue

需要注意的是MR和AR的位置，AR在上，MR在下。

6. Different objectives of businesses-effect on price, output and profit

需要注意的是Profit Max Output是在MC=MR

Revenue Max Output是在MR=0的點上

7. The shut down price for a business in the short run

In the short run the firm will continue to produce as long as total revenue covers total variable costs or put another way, so long as price per unit > or equal to average variable cost (AR = AVC).

The reason for this is as follows. A business』s fixed costs must be paid regardless of the level of output. If we make an assumption that these costs are sunk costs (i.e. they cannot be covered if the firm shuts down) then the loss per unit would be greater if the firm were to shut down, provided variable costs are covered.

In the short run, the supply curve for a competitive firm is the marginal cost curve above average variable cost.

8. Short run and long run in perfect competition

Key Point：No barriers to entry and super normal profits encourage the entry of new firms shifting market supply&price downward until price falls back to P2. Normal profits are restored.

就算公司在短期內盈利，perfect competition的條件下，新公司的進入帶來market suppy增加，長期的話公司只會不盈利也不虧損。

9. Short Run and long run in monopolistic competition

A. Short-Run super normal profits

B. Long run price and output equilibrium with monopolistic competition

In the long run, normal profits are made; average and marginal revenue is affected by the entry of newproducts into the market

10. Oligopoly-the kinked demand curve model

An oligopoly is a market dominated by a few producers, each of which has control over the market. It is an industry where there is a high level of market concentration. However, oligopoly is best defined by the conduct (or behaviour) of firms within a market rather than its market structure.

The kinked demand curve model assumes that a business might face a dual demand curve for its product based on the likely reactions of other firms in the market to a change in its price or another variable. The common assumption is that firms in an oligopoly are looking to protect and maintain market share and that rival firms are unlikely to match another』s price increase but may match a price fall. I.e. rival firms within an oligopoly react asymmetrically to a change in the price of another firm.

The kinked demand curve model therefore makes a prediction that a business might reach a stable profit-maximising equilibrium at price P1 and output Q1 and have little incentive to alter prices. Even a shift in the marginal cost curve (MC1) in the diagram above might not be enough to change the profit maximising equilibrium.

The kinked demand curve model predicts periods of relative price stability under an oligopoly with businesses focusing on non-price competition as a means of reinforcing their market position and increasing their supernormal profits.

最後給大家幾點在考試中畫圖的建議：

把圖畫大，大概A4紙的一半，這樣可以讓圖表更加清晰
不要把解釋擠在圖的周圍，最好空一行在下面開始解釋，這樣可以讓文章更加整齊
標記好每一條線代表了什麼，往哪邊平移
標記好x軸y軸代表了什麼

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