How Prices Affect Consumer Choices

Price is the amount of money required for a buyer to pay to a seller in exchange for goods or services. According to the law of demand, when the price of a good rises, its quantity demanded decreases, and when price falls, quantity demanded increases—assuming other factors remain constant (ceteris paribus).

This inverse relationship exists because of two key effects:

• Substitution effect: When a good's price falls, consumers substitute it for more expensive alternatives
• Income effect: A price fall increases consumers' purchasing power, allowing them to buy more goods

Price Elasticity of Demand

Price elasticity of demand measures how sensitive quantity demanded is to changes in price. It is calculated as:

$e_p^d = \frac{\%\Delta Q^d}{\%\Delta P}$

The value of price elasticity of demand determines how consumers respond to price changes:

Example: If beef price increases from TShs 6,000 to TShs 8,000 per kg and quantity demanded falls from 100,000 kg to 80,000 kg:

$e_p^d = -\left(\frac{\Delta Q}{\Delta P} \times \frac{P_0}{Q_0}\right) = -\left(\frac{-20,000}{2,000} \times \frac{6,000}{100,000}\right) = 0.6$

Since 0.6 < 1, demand for beef is inelastic—consumers are relatively unresponsive to price changes. This means price increases generate higher total revenue for sellers.

How Prices Affect Producer Decisions

According to the law of supply, when the price of a good rises, quantity supplied increases, and when price falls, quantity supplied decreases. This positive relationship exists because higher prices increase profit margins, encouraging producers to supply more.

Price Elasticity of Supply

Price elasticity of supply measures how responsive quantity supplied is to price changes:

$e_p^s = \frac{\%\Delta Q^s}{\%\Delta P}$

Pricing and Profit Maximization

Businesses use price theory to maximize profits through several mechanisms:

1. Revenue calculation: Total revenue (TR) = Price × Quantity. When demand is elastic, lowering price increases total revenue; when inelastic, raising price increases total revenue.

2. Consumer surplus: The difference between what consumers are willing to pay and what they actually pay. A lower price increases consumer surplus.

3. Producer surplus: The difference between the actual price received and the minimum price producers would accept. Higher prices increase producer surplus.

4. Market equilibrium: At equilibrium price, quantity demanded equals quantity supplied, maximizing total welfare in the market.

Worked Example: Pricing Decisions for a Tanzanian Supermarket

A supermarket in Dar es Salaam sells cooking oil. Current price is TShs 3,500 per litre, and quantity demanded is 500 litres per day. The manager considers raising the price to TShs 4,000.

If price elasticity of demand is 0.8 (inelastic):

• A 14.3% price increase would reduce quantity demanded by: 0.8 × 14.3% = 11.44%
• New quantity = 500 × (1 - 0.1144) = 443 litres
• New revenue = TShs 4,000 × 443 = TShs 1,772,000
• Original revenue = TShs 3,500 × 500 = TShs 1,750,000

Since demand is inelastic, raising price increases total revenue and likely profits, assuming costs remain constant.

• Price theory shows how demand and supply interact to determine market prices
• Consumer behaviour: Lower prices encourage more purchases; elasticity determines the magnitude of response
• Business profits: Price changes affect revenue; businesses must consider elasticity when setting prices
• Elasticity helps predict whether price changes will increase or decrease total revenue
• Strategic pricing requires understanding whether demand is elastic or inelastic

A Tanzanian maize farmer deciding when to sell harvested maize uses price theory directly. If the farmer learns that maize demand is inelastic (people must eat regardless of price), raising the selling price during shortage periods may increase total revenue. Conversely, during harvest season when supply is high and prices fall, the farmer may store maize expecting prices to rise later—using knowledge of supply elasticity and price expectations to maximize profit from limited production.