A level微观经济的这10张表你一定要看

考试中大家对图表又爱又恨：它是很关键的得分点，但是有些同学对图表不够熟悉在画图上浪费了很多时间，那微观经济中比较关键的图表都有哪些呢？

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.我们也可以从Marginal Product的角度来想，比如我们假设其他变量不变然后增加Labour的数量，刚开始MP会增加，但后来员工越来越多造成拥挤，MP会慢慢地下降，Total output会上升但是斜率在慢慢下降。

2. Fixed and Variable Costs in the short run

关于FC和VC的要点：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

这里大家需要知道的还包括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=MRRevenue Max Output是在MR=0的点上

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.就算公司在短期内盈利，perfect competition的条件下，新公司的进入带来market suppy增加，长期的话公司只会不盈利也不亏损。

9. Short Run and long run in monopolistic competition

A. Short-Run super normal profits

B. Long run price and output equilibrium with monopolistic competitionIn 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.

最后给大家几点在考试中画图的建议：把图画大，大概A4纸的一半，这样可以让图表更加清晰不要把解释挤在图的周围，最好空一行在下面开始解释，这样可以让文章更加整齐标记好每一条线代表了什么，往哪边平移标记好x轴y轴代表了什么