Revenus et effets de substitution

The substitution effect occurs when a price change alters relative prices, causing consumers to buy more of the cheaper good while maintaining satisfaction. The income effect happens when purchasing power increases due to a lower price, allowing consumers to buy more total goods. Together, these two effects create the total effect of a price change on consumption.

When a product's price decreases, consumers can purchase the same quantity for less money, leaving extra income available for additional purchases. This increase in purchasing power, or real income, allows consumers to buy more total items than before. The income effect captures this consumption response to higher purchasing power.

When a good's price decreases relative to other goods, its relative price changes, making it more attractive compared to alternatives. Consumers substitute the now-cheaper good for other goods to maintain their satisfaction level while minimizing spending. This substitution response reflects how relative price changes influence consumption choices.

The total effect is the combined impact of price changes on consumption, consisting of both the substitution effect and income effect. It shows the complete change in quantity purchased when a good's price changes. The total effect represents the actual shift in consumer equilibrium from the original consumption point to the new one.

The substitution effect is shown by drawing a budget line parallel to the new price ratio, tangent to the original indifference curve. The movement from the original equilibrium point to this tangent point represents the substitution effect, isolating the impact of relative price changes while holding satisfaction constant.

When both effects work together, consumption of the cheaper good increases substantially. For example, if a book's price drops, consumers buy more books due to lower relative prices and increased purchasing power. This combined effect produces a larger total consumption change than either effect alone.

Income and substitution effects explain how consumers respond to price changes, which is fundamental to understanding demand behavior. By decomposing the total effect into these components, economists can predict whether demand increases or decreases and by how much. This analysis is essential for deriving accurate demand curves from consumer choices.