AP Microeconomics: Monopsony – Characteristics and Graph

AP Microeconomics – Monopsony – Characteristics and Graph

AP Microeconomics – Monopsony: Characteristics & Graph

What This Is

A monopsony is a market where a single buyer (most often a single employer) faces the entire supply of a factor of production—usually labor. Because the buyer is “the only game in town,” it can set a lower price (wage) than would exist in a competitive labor market. Understanding monopsony is essential for the AP?Micro exam because you’ll be asked to draw the labor?market diagram, calculate the dead?weight loss, and evaluate policies such as a minimum wage or a “living?wage” ordinance.

Real?world example: The U.S. Department of Defense is the sole purchaser of military?grade steel; a small mining town where the local coal company is the only major employer; or a university town where the university is the only large employer of graduate assistants.

Key Terms & Formulas

• Monopsony (Labor?Market Diagram) – Graph with Wage (W) on the vertical axis and Quantity of Labor (L) on the horizontal axis. The upward?sloping Labor Supply (S?) curve is the same as the competitive Supply of Labor.
• Marginal Factor Cost (MFC) – The additional cost of hiring one more unit of labor. Formula: MFC = ?(TC)/?L = W + (?W/?L)·L. In a monopsony, the MFC curve lies above the labor?supply curve and has twice the slope of S?.
• Value of Marginal Product of Labor (VMPL) – Revenue generated by the last worker hired. Formula: VMPL = MR × MP? (or P × MP? in a perfectly competitive product market).
• Profit?Maximizing Condition (Monopsony) – MFC = VMPL. The monopsonist hires labor where its marginal cost equals the value of the marginal product.
• Competitive Labor Market Equilibrium – Occurs where S? = VMPL; the wage equals the marginal product of labor.
• Dead?Weight Loss (DWL) from Monopsony – Area of the triangle between S?, MFC, and VMPL. Formula: DWL = ½·(L? – L?)·(W? – W?) where superscripts c = competitive, m = monopsony.
• Minimum Wage in a Monopsony – A binding minimum wage set above the monopsony wage but below the competitive wage can increase employment and reduce DWL.
• Shift Shifters of Labor Supply – Changes in population, alternative job opportunities, or education/training programs shift the S? curve left (decrease) or right (increase).
• Elasticity of Labor Supply – Elasticity = %?L / %?W; a more elastic supply makes the MFC curve flatter, reducing monopsony power.

Step?by?Step / Process Flow (Typical FRQ)

1. Draw the axes – Wage (vertical) vs. Quantity of Labor (horizontal).
2. Plot the Labor Supply curve (S?) – Upward sloping, starting at the origin.
3. Derive the MFC curve – From the supply curve, double the slope; label it MFC and show it lying above S?.
4. Add the VMPL curve – Usually a downward?sloping line (or a horizontal line if product price is constant).
5. Find the monopsony equilibrium – Locate the intersection of MFC and VMPL; drop a vertical line to the wage axis (this is the monopsony wage W?) and a horizontal line to the labor axis (employment L?).
6. Identify the competitive equilibrium – Intersection of S? and VMPL; label wage W? and employment L?.
7. Shade the dead?weight loss – The triangular area between S?, MFC, and VMPL (from L? to L?).
8. Answer the prompt – Explain why the monopsonist hires fewer workers at a lower wage, how a minimum wage would affect the diagram, and calculate DWL if numbers are given.

Common Mistakes

AP Exam Insights

1. Graph?Only FRQs – You’ll be asked to draw the monopsony diagram, label S?, MFC, VMPL, the two equilibria, and the dead?weight loss. No need for a title; just label each curve clearly.
2. Policy?Impact Questions – The exam often asks how a binding minimum wage or a “living?wage” ordinance changes the diagram. Remember: in a monopsony, a modest minimum wage can increase employment (the opposite of the competitive case).
3. Quantitative Calculations – When given numbers for wages and quantities, compute the dead?weight loss using the triangle formula. AP graders look for the correct set?up (½·base·height) and proper units.
4. Conceptual Multiple?Choice – Items may test the definition of MFC, the direction of a shift in labor supply, or the effect of a more elastic labor supply on monopsony power. Choose the answer that mentions the steeper MFC curve or reduced DWL.

Quick Check Questions

1. MC: In a town where the only employer is a large steel mill, the labor?supply curve is upward sloping. Which of the following statements is true?
2. A) The firm’s marginal factor cost curve coincides with the labor?supply curve.
3. B) The firm will hire workers where MFC = VMPL, which occurs at a lower wage than the competitive equilibrium.
4. C) A binding minimum wage set above the competitive wage will reduce employment.

5. Answer: B – The monopsonist equates MFC (which lies above the supply curve) with VMPL, resulting in a lower wage and lower employment than in a competitive market.

6. FRQ?style: A monopsonist hires 80 workers at a wage of $12. The competitive equilibrium would be 120 workers at $15. Calculate the dead?weight loss.

7. Answer: DWL = ½·(120?80)·(15?12) = ½·40·3 = $60 (in the same monetary units as the problem).

8. MC: If the labor?supply curve becomes more elastic, the monopsonist’s market power:

9. A) Increases, because MFC rises faster.
10. B) Decreases, because MFC gets closer to the supply curve.
11. C) Remains unchanged, because elasticity does not affect wages.
12. Answer: B – A flatter (more elastic) supply curve makes MFC less steep, reducing the wage?cutting ability of the monopsonist.

Last?Minute Cram Sheet

1. Monopsony = one buyer of a factor (usually labor).
2. MFC curve lies above the labor?supply curve and has twice the slope of S?.
3. Profit?max rule: MFC = VMPL (not MFC = MR of the product).
4. Competitive equilibrium: S? = VMPL-wage = marginal product.
5. DWL formula: ½·(LL?)·(WW?).
6. Minimum wage in monopsony can raise both wage and employment if set between W? and W?.
7. Elastic labor supply-weaker monopsony power (MFC flatter).
8. Axes: vertical = Wage (W), horizontal = Quantity of Labor (L).
9. Shift shifters: population, alternative jobs, education-move S? left/right.
10. “Supply increases” = curve shifts right, not up; a movement along the curve is caused by a wage change.

Good luck—draw clean diagrams, label every curve, and remember the “monopsony wage is lower, employment is lower, and a modest minimum wage can improve both”!