2.14
Élasticité de la demande par la méthode du point milieu
Au point A, le prix est de 6 $ pour 120 unités. En passant au point B, le prix augmente à 9 $, ce qui entraîne une diminution de la quantité demandée…
Considérons deux points sur une courbe de demande : le point A et le point B.
Au point A, le prix est de 6 dollars, et la quantité demandée est de 120 unités.
Au point B, le prix monte à 9 dollars, et la quantité demandée diminue à 80 unités.
D’un point A à un point B, le prix augmente de 50 % et la quantité demandée diminue de 33,33 %. Cela donne une élasticité-prix de 33,33 sur 50.
Cependant, d’un point B à un point A, le prix diminue de 33,33 % et la quantité demandée augmente de 50 %. Cela donne une élasticité-prix de 50 sur 33,33.
Cet écart est dû aux différentes bases utilisées dans chaque direction. Elle peut être évitée en calculant l’élasticité des prix à l’aide de la méthode du point médian.
Ici, les variations de la quantité demandée et du prix sont divisées par leurs points médians respectifs.
Dans l’exemple, le point médian du prix est de 7,5 dollars et le point médian de la quantité demandée est de 100 unités.
À partir de la méthode du point médian, le prix change de 40 % et la quantité demandée change du même pourcentage, ce qui donne une élasticité des prix égale à 1.
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Q1: Why does price elasticity differ when moving between two demand curve points in different directions?
Price elasticity calculations yield different results depending on direction because they use different bases for percentage changes. Moving from point A to B uses one base, while moving from B to A uses another. For example, a price change from $6 to $9 represents a 50% increase, but $9 to $6 is only a 33.33% decrease. This directional inconsistency creates conflicting elasticity values without a standardized calculation method.
Q2: What is the midpoint method and how does it solve elasticity calculation problems?
The midpoint method calculates price elasticity by dividing percentage changes in quantity and price by their respective midpoints rather than starting points. This approach eliminates directional bias and produces consistent elasticity values regardless of movement direction. Using midpoints ensures a standardized base, making elasticity measurements comparable and reliable across different demand curve analyses.
Q3: How do you calculate midpoint values for price and quantity in elasticity analysis?
Midpoint values are calculated by averaging the two points. For price, add both prices and divide by two: ($6 + $9) / 2 = $7.50. For quantity, add both quantities and divide by two: (120 + 80) / 2 = 100 units. These midpoints serve as the denominator when calculating percentage changes, ensuring consistent elasticity measurements regardless of which direction you move along the demand curve.
Q4: What percentage changes result from applying the midpoint method to the example data?
Using the midpoint method with a midpoint price of $7.50 and midpoint quantity of 100 units, the price change is calculated as (9 - 6) / 7.50 = 40%, and the quantity change is (80 - 120) / 100 = 40%. Both changes equal 40%, resulting in a price elasticity of 1. This consistency demonstrates the midpoint method's advantage over directional calculations that produce different elasticity values.
Q5: How does the midpoint method compare to calculating elasticity in different directions?
The directional approach yields elasticity of 0.67 moving from A to B and 1.5 moving from B to A. The midpoint method produces a consistent elasticity of 1 regardless of direction. This consistency makes the midpoint method superior for economic analysis because it provides a single, reliable measure of elasticity. Understanding degrees of elasticity of demand and the demand graph helps interpret these values in context.
Q6: Why is consistency important when measuring price elasticity of demand?
Consistent elasticity measurements allow economists to accurately compare demand responsiveness across different products, markets, and time periods. Without standardization, conflicting elasticity values create confusion and unreliable economic analysis. The midpoint method provides this consistency by using a neutral base, enabling meaningful comparisons of how quantity demanded responds to price changes across various economic scenarios.
Q7: What does an elasticity value of 1 indicate about demand responsiveness?
An elasticity value of 1 indicates unit elasticity, meaning quantity demanded changes by the same percentage as price. In the example, a 40% price change produces a 40% quantity change, resulting in elasticity of 1. This represents the midpoint between elastic demand (elasticity > 1) and inelastic demand (elasticity < 1), showing proportional responsiveness to price changes.