Labour Market: MRP — Edexcel A-level Economics

SPEC 3.5 • LABOUR MARKET

Labour Market: MRP & Wage Determination

Derived demand, marginal revenue product, competitive equilibrium, supply & demand shifters, elasticity of labour demand, and wage differentials

Key Definitions

Derived Demand

The demand for labour is derived from the demand for the goods and services it produces. If demand for a product rises, the demand for the labour that produces it also rises.

Marginal Revenue Product (MRP)

The additional revenue a firm gains from employing one more worker. The MRP curve is the firm's demand curve for labour.

MRP = Marginal Physical Product (MPP) × Price of Output

The Hiring Rule

A firm will employ an extra worker as long as MRP ≥ Wage. Profit-maximising employment is where MRP = Wage.

Why the MRP Curve Slopes Downward

The MRP curve falls because of diminishing marginal returns. As more workers are added to fixed capital, each additional worker's physical product eventually declines — so MRP falls.

More workers added to fixed capital

Diminishing marginal returns

MPP falls

MRP = MPP × P falls

DL slopes downward

Worked Example — MRP Calculation

WorkersTotal OutputMPPPrice (£)MRP (£)150501050021106010600315040104004180301030052002010200If the wage is £300/day, the firm hires 4 workers (MRP ≥ wage). The 5th worker's MRP (£200) is below the wage — not hired.

Demand for Labour — Shifters

Five factors shift the DL curve. Remember: these shift the entire curve, not movement along it (which is caused by wage changes).

Five DL Shifters

Change in demand for the product — higher product demand → higher MRP → DL shifts right

Change in labour productivity — more productive workers → higher MPP → MRP rises → DL shifts right

Change in the price of output — higher output price → MRP rises → DL shifts right

Change in the price of capital — cheaper capital → firms substitute away from labour → DL shifts left

Changes in technology — automation may reduce demand for some labour but increase demand for skilled workers

Exam Tip

The first three all work through MRP. If the question says "explain why wages have risen", check whether it's a DL shift (MRP change) or an SL shift (worker availability change). This determines which diagram to draw.

Supply of Labour — Shifters

The supply of labour to a particular occupation normally slopes upward — higher wages attract more workers. Six factors shift the entire SL curve.

Six SL Shifters

Wages in alternative occupations — if rival wages rise, SL shifts left as workers leave

Non-monetary benefits — good working conditions, prestige, job security → SL shifts right

Qualifications & barriers to entry — high skill requirements restrict supply → SL more inelastic

Size of working population — immigration, demographic changes, participation rate → SL shifts

Geographical & occupational immobility — frictions reduce supply responses

Net migration — inward migration → SL shifts right; emigration → SL shifts left

Backward-Bending Supply

At very high wage levels, the supply curve can bend backward. Workers choose leisure over extra income — the income effect outweighs the substitution effect. Occasionally tested in multiple choice.

Competitive Labour Market Equilibrium

In a competitive labour market, the wage is determined by the intersection of DL (= MRP) and SL. No single firm or worker has market power.

Key Point

At W*, the quantity of labour demanded equals the quantity supplied. Every worker is paid their marginal revenue product. There is no exploitation — this is the benchmark against which monopsony is compared.

Shift Example — SL Shifts Left

Context (Nov 2021 P1): Polish engineers emigrate for higher-paid jobs abroad. Supply of engineers shifts left.

Engineers emigrate

SL shifts left

Excess demand at W*

Firms bid wages up

W₁ > W*, L₁ < L*

Exam Tip

This chain of reasoning — shift → excess demand/supply → wage adjustment → new equilibrium — is the Level 3 template for any 4-mark labour market question. Always state all steps.

Elasticity of Labour Demand

The elasticity of demand for labour determines how much employment changes when wages change. This is the key evaluation point for minimum wage questions.

DL More Elastic When

Labour costs are a high proportion of total costs

Easy to substitute capital for labour

Demand for the final product is elastic

In the long run (substitution possible)

DL More Inelastic When

Labour is a small share of total costs

Work requires specialist skills (hard to replace)

Demand for final product is inelastic

In the short run (can't easily automate)

Examiner Alert

If a minimum wage question doesn't discuss elasticity of DL, it scores maximum Level 2. Always state: "The employment effect depends critically on the elasticity of demand for labour in this sector."

Causes of Wage Differentials

Why do some workers earn more than others? Seven causes — all required for the spec.

#CauseExplanation

1Differences in MRPHigher-skilled workers produce more revenue → higher wages (surgeons vs retail workers)

2Compensating differentialsUnpleasant, dangerous, or antisocial work commands a wage premium (night shifts, mining)

3Barriers to entry / qualificationsProfessions requiring years of training restrict SL → higher wages (doctors, lawyers)

4DiscriminationGender, ethnicity, age pay gaps persist due to labour market discrimination

5Trade union powerUnionised workers earn wage premiums (~10–15% in UK); non-unionised sectors lower

6Monopsony powerEmployers with buying power suppress wages below competitive levels

7Geographical differencesRegional cost-of-living and labour demand variations create regional pay gaps

Government Responses to Wage Inequality

Policy Tools

National Living Wage — sets a wage floor for adult workers

Progressive income tax — redistributes from higher to lower earners

In-work benefits (Universal Credit) — supports low-income households

Education & training — addresses skills gap driving structural wage differentials

Anti-discrimination legislation — Equality Act 2010, gender pay gap reporting

Evaluation

Do interventions actually reduce inequality, or create new distortions? The Laffer Curve suggests very high marginal tax rates may reduce work incentives and ultimately reduce tax revenue — though the empirical threshold is contested. Minimum wages may cause unemployment if set too high. Education investment takes years to affect labour supply.

Common Errors — From Examiner Reports

Examiner Alert — Labour Market Diagrams

Wrong axis labels — must be "Wage Rate" (vertical) and "Quantity of Labour" (horizontal), NOT Price/Quantity

Not labelling DL as MRP — write "DL = MRP" to show you understand derived demand

Confusing movement along with shift — a wage change = movement along; other factors = shift

Forgetting to show the chain of reasoning — shift → excess demand/supply → wage adjustment → new equilibrium

Examiner Alert — MRP Questions

Forgetting the formula — always state MRP = MPP × Price before calculating

Not linking MRP to diminishing returns — explain WHY MRP falls (diminishing marginal returns to labour)

Not stating the hiring rule — firm employs workers up to where MRP = Wage

Practice Question

Question (4 marks): With reference to the data, explain how the emigration of engineers from Poland is likely to affect the wage rate and employment of engineers remaining in Poland. Use a diagram in your answer.

1

Identify the shift: Emigration of engineers reduces the supply of labour to Poland's engineering sector. SL shifts left (SL → SL₁). (1 mark)

2

Explain the mechanism: At the original equilibrium wage W*, there is now excess demand for engineers — more jobs than workers available. (1 mark)

3

State the outcome: Firms compete to hire from the smaller pool, bidding wages up. New equilibrium: W₁ > W* (wages rise), L₁ < L* (employment falls). (1 mark)

4

Diagram: Labour market diagram with correctly labelled axes (Wage Rate / Quantity of Labour), DL = MRP, SL shifting left to SL₁, showing W₁ > W* and L₁ < L*. (1 mark)

Summary

Key Facts

ConceptDetail

Derived demandDL comes from demand for the product labour produces

MRP formulaMRP = MPP × Price of output

Hiring ruleEmploy workers up to MRP = Wage

Why MRP fallsDiminishing marginal returns → MPP falls → MRP falls

Competitive equilibriumW* where DL (MRP) = SL. Workers paid their MRP.

DL shiftersProduct demand, productivity, output price, capital price, technology

SL shiftersAlternative wages, non-monetary benefits, qualifications, population, immobility, migration

Wage Differentials (7 causes)

MRP differences

Compensating differentials

Qualifications / barriers

Discrimination

Trade union power

Monopsony power

Geography

Diagram Checklist

✓ Axes: Wage Rate / Quantity of Labour

✓ DL = MRP (downward sloping)

✓ SL (upward sloping)

✓ W* and L* at intersection

✓ Show shift + new equilibrium

✓ Label W₁, L₁ clearly

The Golden Rule

Labour markets use the same supply and demand logic as goods markets — but with different axis labels. The biggest exam error is mislabelling axes. Always write "Wage Rate" on the vertical axis and "Quantity of Labour" on the horizontal axis.