The demand for a good depends on several factors, such as price of the good, perceived Quality, Advertising, income, confidence of consumers and changes in taste and fashion.

对一种商品的需求取决于几个因素，如商品的价格、感知的质量、广告、收入、消费者的信心以及品味和时尚的变化。

We can look at either an individual demand curve or the total demand in the economy. 我们可以看一下个人需求曲线或经济中的总需求。

• The individual demand curve illustrates the price people are willing to pay for a particular quantity of a good. 个人需求曲线说明了人们愿意为某一特定数量的商品支付的价格。
• The market demand curve will be the sum of all individual demand curves. It shows the quantity of a good consumers plan to buy at different prices. 市场需求曲线将是所有个人需求曲线的总和。它显示了消费者在不同价格下计划购买的商品的数量。

1. Change in price 价格的变化

A change in price causes a movement along the Demand Curve. 价格的变化会导致需求曲线的移动。

For example, if there is an increase in price from $12 to ￡16 then there will be a fall in demand from 80 to 60. 例如，如果价格从12美元增加到16英镑，那么需求就会从80下降到60。

How important is price? 价格有多重要？

Some goods are more affected by price than others. 有些商品受价格的影响比其他商品大。

• If petrol increases in price, because it is a necessity, there is only a small fall in demand (we say it is inelastic demand). 如果汽油涨价，因为它是一种必需品，需求只会有小幅下降（我们说它是无弹性需求）。
• If Volvic water increases in price, there will be a significant fall in demand because people buy cheaper substitutes (demand is elastic) 如果VOLVIC水涨价，需求就会大幅下降，因为人们会购买更便宜的替代品（需求有弹性）。

Shifts in the demand curve 需求曲线的变化

This occurs when, even at the same price, consumers are willing to buy a higher (or lower) quantity of goods. This will occur if there is a shift in the conditions of demand. 当即使在相同的价格下，消费者也愿意购买更多（或更少）的商品时，就会出现这种情况。如果需求条件发生了变化，就会出现这种情况。

Even at the same price of $12, more is demanded. 即使在12美元的相同价格下，也会有更多的需求。

Factors which can shift the demand curve 能使需求曲线移动的因素

A shift to the right in the demand curve can occur for a number of reasons 需求曲线向右移动的原因有很多:

1. Income 收入. An increase in disposable income enabling consumers to be able to afford more goods. Higher income could occur for a variety of reasons, such as higher wages and lower taxes. 可支配收入的增加使消费者能够买得起更多的商品。收入增加有多种原因，如工资增加和税收减少。
2. Credit facilities 信贷设施. If it is easier and cheaper to borrow, this may encourage consumers to buy expensive items on credit, for example, cars and foreign holidays. 如果贷款更容易、更便宜，这可能会鼓励消费者赊账购买昂贵的物品，例如汽车和国外度假。
3. Quality 质量. An increase in the quality of the good e.g. better quality digital cameras encourages people to buy one. 商品质量的提高，如质量更好的数码相机，会鼓励人们去购买。
4. Advertising 广告 can increase brand loyalty to goods and increase demand. For example, higher spending on advertising by Coca Cola has increased global sales. 可以提高商品的品牌忠诚度，增加需求。例如，可口可乐公司在广告上的更高支出增加了全球销售。
5. Substitutes 替代品. An increase in the price of substitutes, e.g. if the price of Samsung mobile phones increases, this will increase the demand for Apple iPhones – a major substitute for the Samsung. 替代品价格的上升，例如，如果三星手机的价格上升，这将增加对苹果iPhone手机的需求–这是三星手机的主要替代品。
6. Complements 补充品. A fall in the price of complements will increase demand. E.g. a lower price of Play Station 2 will increase the demand for compatible Play Station games. 补充品价格的下降将增加需求。例如，Play Station 2的价格降低将增加对兼容Play Station游戏的需求。
7. Weather 天气: In cold weather, there will be increased demand for fuel and warm weather clothes. 在寒冷的天气里，对燃料和保暖衣服的需求会增加。
8. Expectations of future price increases 对未来价格上涨的预期. A commodity like gold may be bought due to speculative reasons; if you think it might go up in the future, you will buy now. 像黄金这样的商品可能由于投机的原因而被购买；如果你认为它在未来可能会上涨，你现在就会购买。
9. Change in circumstances 情况的变化. The Covid lockdown of 2020/21 led to a significant fall in demand for leisure and going out to the cinema, but it led to a boom in demand for electrical goods, like TVs and Netflix subscriptions. 2020/21年的Covid封锁导致休闲和外出看电影的需求大幅下降，但它导致了电视和Netflix订阅等电器商品需求的繁荣。
10. Economic cycle 经济周期. In a recession, people will cut back on spending, even if their income remains steady. This is because they fear the possibility of losing job, so they will take risk averse approach and reduce spending. Similarly in an economic boom, confidence will be high and incomes rising – causing more demand 在经济衰退中，即使收入保持稳定，人们也会削减开支。这是因为他们担心失去工作的可能性，所以他们会采取规避风险的方法，减少支出。同样，在经济繁荣时期，人们的信心会很高，收入也会增加–导致更多需求。
11. Wealth-effect 财富效应. If households experience an increase in their wealth (e.g. house prices rise), then they will be more willing to spend. This is because they can re-mortgage their house to get equity withdrawal and/or they will feel more confidence because they own more assets. 如果家庭的财富增加（如房价上涨），那么他们就会更愿意消费。这是因为他们可以重新抵押他们的房子，以获得股权退出，和/或他们会感到更有信心，因为他们拥有更多的资产。

Fall in demand 需求下降

A fall in demand could occur due to lower disposable income or decline in the popularity of the good. 需求下降可能是由于可支配收入减少或商品的受欢迎程度下降。

Evaluation 评价

• For some luxury goods, income will be an important determinant of demand. e.g. if your income increased you would buy more restaurant meals, but probably not more salt. 例如，如果你的收入增加，你就会购买更多的餐厅膳食，但可能不会购买更多的盐。
• Advertising is important for goods in which branding is important, e.g. soft drinks but not for bananas. 广告对那些品牌效应很重要的商品来说是很重要的，例如软饮料，但对香蕉来说不是。

Other types of demand 其他类型的需求

• Effective demand 有效需求: This occurs when a consumers desire to buy a good can be backed up by his ability to afford it. 当消费者购买商品的愿望能够得到他的支付能力的支持时，就会出现这种需求。
• Derived demand 派生需求: This occurs when a good or factor of production such as labour is demanded for another reason 当一种商品或生产要素（如劳动力）因其他原因而被需求时，就会出现这种需求。
• A Giffen good is a good where an increase in price of a basic item leads to an increase in demand, because very poor people cannot afford any other luxury goods. 吉芬商品是一种基本物品的价格上涨导致需求增加的商品，因为非常贫穷的人买不起任何其他奢侈品。
• An ostentatious good, is a good where an increase in price leads to an increase in demand because people believe it is now better. 炫耀性商品，是指价格上涨导致需求增加的商品，因为人们相信它现在更好。
• Composite demand 复合需求 – A good which is demanded for multiple different uses 一种被要求用于多种不同用途的商品。
• Joint demand 联合需求 – goods bought together e.g. printer and printer ink. 一起购买的商品，例如，打印机和打印机墨水。