Law of demand
In microeconomics, the law of demand is a fundamental principle which states that there is an inverse relationship between price and quantity demanded. In other words, "conditional on all else being equal, as the price of a good increases ', quantity demanded will decrease '; conversely, as the price of a good decreases ', quantity demanded will increase '". Alfred Marshall worded this as: "When we say that a person's demand for anything increases, we mean that he will buy more of it than he would before at the same price, and that he will buy as much of it as before at a higher price". The law of demand, however, only makes a qualitative statement in the sense that it describes the direction of change in the amount of quantity demanded but not the magnitude of change.
The law of demand is represented by a graph called the demand curve, with quantity demanded on the x-axis and price on the y-axis. Demand curves are downward sloping by definition of the law of demand. The law of demand also works together with the law of supply to determine the efficient allocation of resources in an economy through the equilibrium price and quantity.
The relationship between price and quantity demanded holds true so long as it is complied with the ceteris paribus condition "all else remain equal" quantity demanded varies inversely with price when income and the prices of other goods remain constant. If all else are not held equal, the law of demand may not necessarily hold. In the real world, there are many determinants of demand other than price, such as the prices of other goods, the consumer's income, preferences etc. There are also exceptions to the law of demand such as Giffen goods and perfectly inelastic goods.
Overview
Economist Alfred Marshall provided the graphical illustration of the law of demand. This graphical illustration is still used today to define and explain a variety of other concepts and theories in economics. A simple explanation of the law of demand is that all else equal, at a higher price, consumer will demand less quantity of a good and vice versa. The law of demand applies to a variety of organisational and business situations. Price determination, government policy formation etc are examples. Together with the law of supply, the law of demand provides to us the equilibrium price and quantity. Moreover, the law of demand and supply explains why goods are priced at the level that they are. They also help us identify opportunities to buy what are perceived to be underpriced goods or assets.Law of Demand is relied heavily upon by managerial economics, which is a branch of economics that applies microeconomic analysis to managerial decision-making, to make informed decisions on pricing, production, and marketing strategies. In this context, understanding the alternative factors that influence the Law of Demand becomes crucial for managers and decision-makers.
- Income effect: The income effect is the change in the quantity demanded of a good or service as a result of changes in consumers' purchasing power. When prices increase, the purchasing power of consumers decreases, leading to a decline in the quantity demanded. Conversely, a decrease in prices will increase purchasing power and lead to an increase in the quantity demanded.
- Substitution effect: The substitution effect is the change in the quantity demanded of a good or service due to a change in the relative prices of substitute goods. When the price of a good increases, consumers may shift their consumption to relatively cheaper substitute goods, causing the demand for the original good to decrease.
- Price expectations: Consumer expectations about future prices can influence their current demand for goods or services. If consumers expect prices to rise in the future, they may increase their current consumption to avoid higher prices later. Conversely, if they expect prices to fall, they may delay consumption, causing a decline in the quantity demanded.
- Market size and demographics: The size of the market and its demographics can also influence the Law of Demand. Changes in population size, age distribution, and income levels can affect the overall demand for goods or services, thus impacting the relationship between price and quantity demanded.
The four main types of elasticity of demand are price elasticity of demand, cross elasticity of demand, income elasticity of demand, and advertising elasticity of demand.
History
The famous law of demand was first stated by Charles Davenant in his essay, "Probable Methods of Making People Gainers in the Balance of Trade ". However, there were instances of its understanding and use much earlier when Gregory King made a demonstration of the law of demand. He represented a relationship between the price of wheat and the harvest where the results suggested that if the harvest falls by 50%, the price would rise by 500%. This demonstration illustrated the law of demand as well as its elasticity.Skipping forward to 1890, economist Alfred Marshall documented the graphical illustration of the law of demand. In Principles of Economics, Alfred Marshall reconciled the demand and supply into a single analytical framework. The formulation of the demand curve was provided by the utility theory while supply curve was determined by the cost. This idea of demand and supply curve is what we still use today to develop the market equilibrium and to support a variety of other economic theories and concepts. Due to general agreement with the observation, economists have come to accept the validity of the law under most situations. Economist also see Alfred Marshall as the pioneer of the standard demand and supply diagrams and their use in economic analysis including welfare applications and consumer surplus.
Mathematical description
Consider the function, where is the quantity demanded of good ', is the demand function, <The law of demand states that. Here is the partial derivative operator.
The above equation, when plotted with quantity demanded on the '-axis and price on the -axis, gives the demand curve, which is also known as the demand schedule. The demand curve is downward sloping illustrating the inverse relationship between quantity demanded and price. Therefore, a downward sloping demand curve embeds the law of demand.
In a more specific manner:
Which is a functional relationship where the quantity demanded by the consumer depends on the price of the good, the monetary income of the consumer, the prices of other goods, and the taste of the consumer.
Another common way to express the law of demand without imposing a functional form is the following:
This formula states that, for all possible prices p' and p, and corresponding demands x' and x, prices and demand must move in opposite directions, i.e. as price increases, demand must decrease and vice versa. Note that demands are demand bundles, not individual demands. Demand for a single good can still increase even though its price also increased, if there is another good whose price increased and which is sufficiently substituted away from. If good i is a Giffen good whose price increases while other goods' prices are held fixed, the law of demand is clearly violated, as we have both and , so that.
Demand versus supply
On the one hand, demand refers to the demand curve. Changes in supply are depicted graphically by a shift in the supply curve to the left or right. Changes in the demand curve are usually caused by 5 major factors, namely: number of buyers, consumer income, tastes or preferences, price of related goods and future expectations.On the other hand, quantity demanded refers to a specific point located on the demand curve which corresponds to a specific price. Therefore, quantity demanded represents the exact quantity of a good or service demanded by a consumer at a particular price, conditional on the other determinants. A change in quantity demanded can be indicated by a movement along the existing demand curve that is caused only by a change in price.
For instance, let's take the example of a housing market. An increase or decrease in price of housing will not shift the demand curve rather it will cause a movement along the demand curve for housing i.e. change in quantity demanded. But if we look at mortgage rates, even if housing prices remain unchanged, an increased mortgage rate leads to a lower willingness to buy at all prices, shifting the demand curve to the left. Consumers will buy less, even though the price is the same. On the other hand, lower mortgage rate leads to a higher willingness to buy at all prices, and eventually shifting the demand curve to the right. Consumers will now buy more, even though the price has not changed at all. Such variation in demand can be explained by demand elasticity.