AQA A-Level Economics (7136)

## Learning Outcomes

- Understand why the demand for labour is a **derived demand**
- Explain **marginal productivity theory** and the formula **MRPL = MPL × MR**
- Distinguish clearly between **marginal physical product of labour** and **marginal revenue product of labour**
- Explain why the firm's demand curve for labour slopes downward
- Apply the profit-maximising rule that a firm employs labour up to the point where **wage = MRPL** in a competitive labour market
- Identify factors that cause a movement along, or a shift of, the labour demand curve
- Evaluate the assumptions and limits of marginal productivity theory in exam answers

## AQA A-Level Economics (7136) Syllabus

For the AQA A-Level Economics (7136), you are expected to understand demand for labour and marginal productivity theory, with a focus on the following syllabus points:

- Know that the demand for labour is a **derived demand** from demand for the final product
- Define **marginal physical product of labour (MPL or MPPL)** as the extra output from one more worker
- Define **marginal revenue product of labour (MRPL)** as the extra revenue from one more worker
- Use the formula **MRPL = MPL × MR**
- Understand that under perfect competition in the product market, **MR = price**, so **MRPL = MPL × price**
- Explain why the firm's labour demand curve is its **MRPL** curve
- Explain the profit-maximising employment rule in a competitive labour market: **wage = MRPL**
- Distinguish between a **movement along** labour demand caused by a wage change and a **shift** in labour demand caused by factors such as productivity or product demand

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. Why is the demand for labour described as a derived demand?
2. What is the difference between **MPL** and **MRPL**?
3. Why does a firm's demand curve for labour usually slope downward?
4. Under perfect competition in the product market, how is **MRPL** calculated?
5. What is the profit-maximising rule for employing labour in a competitive labour market?

## Introduction

Firms do not hire workers for their own sake. They hire workers because those workers help produce goods and services that can be sold. This is the starting point for understanding the demand for labour.

For AQA Economics, this topic is very testable because it links formula work, diagram logic and applied analysis. You need to explain both the basic theory and the conditions under which it works well or less well. In Paper 3 especially, this can be linked to business costs, productivity, market structure and employment.

> **Key Term: derived demand**
> Demand for a factor of production that exists because there is demand for the goods or services it helps to produce.

### Derived demand and the basic logic of labour demand

A firm's demand for labour depends on what labour helps the firm to earn. If consumers buy more holidays, airlines may need more pilots and cabin crew. If demand for restaurant meals falls, restaurants may hire fewer chefs and waiting staff. Labour demand therefore comes from demand in the product market.

This is why labour demand is not the same as consumer demand. Households demand goods directly. Firms demand labour indirectly, because labour helps produce saleable output.

A useful exam distinction is between **derived demand** and **composite demand**. Derived demand means labour is wanted because of the output it helps create. Composite demand means a good has more than one use. Labour demand is about derived demand.

> **Key Term: demand for labour**
> The number of workers firms are willing and able to employ at a given wage rate over a period of time.

The quantity of labour demanded will usually fall when the wage rate rises, other things equal. This gives a downward-sloping labour demand curve. But for high-mark answers, do not stop there. You must explain why firms reduce hiring when wages rise: they compare the extra cost of a worker with the extra revenue that worker generates.

> **Test Tip:** In short-answer questions, do not define labour demand as “how many people want jobs.” Labour demand comes from firms, not workers.

### Marginal productivity theory: MPL, MR and MRPL

Marginal productivity theory explains labour demand through the extra contribution of one more worker.

First, think about the extra output created by an additional worker.

> **Key Term: marginal physical product of labour (MPL)**
> The extra output produced by employing one more worker, with other factors unchanged.

If a bakery increases its workforce from 5 bakers to 6 and output rises from 200 loaves to 230 loaves per day, the sixth worker's MPL is **30 loaves**.

However, firms care about revenue, not just output. So we convert extra output into extra revenue.

> **Key Term: marginal revenue product of labour (MRPL)**
> The extra revenue gained by a firm from employing one more worker.

The formula is:

MRPL = MPL × MR

where **MR** is marginal revenue, the extra revenue from selling one more unit of output.

Under perfect competition in the product market, the firm is a price taker, so:

MR = price

Therefore:

MRPL = MPL × price

This is the standard AQA version used in many labour-demand questions.

Worked example:

A firm employs one extra worker.

- Extra output produced by the worker = **8 units**
- Selling price per unit = **£15**
- Under perfect competition, **MR = £15**

Step 1: Identify MPL  
MPL = **8**

Step 2: Identify MR  
MR = **£15**

Step 3: Apply the formula  
MRPL = MPL × MR  
MRPL = 8 × 15  
MRPL = **£120**

So the extra worker adds **£120** to revenue.

If the wage paid to that worker is below **£120**, employing the worker adds to profit. If the wage is above **£120**, employing that worker reduces profit.

A second worked example using a small schedule:

| Workers | Total output | MPL | Price | MRPL |
| ------- | -----------: | --: | ----: | ---: |
| 1       |           10 |  10 |    £5 |  £50 |
| 2       |           18 |   8 |    £5 |  £40 |
| 3       |           24 |   6 |    £5 |  £30 |
| 4       |           28 |   4 |    £5 |  £20 |

Here, MPL falls as more workers are hired. Because price stays constant at **£5**, MRPL also falls. The **MRPL** curve therefore has the same basic shape as the **MPL** curve under perfect competition in the product market.

> **Key Term: marginal revenue (MR)**
> The addition to total revenue from selling one more unit of output.

Common student errors:

- Confusing **MPL** with **MRPL**. MPL is measured in units of output; MRPL is measured in money.
- Writing **MRPL = wage × MPL**. The correct formula is **MRPL = MPL × MR**.
- Forgetting that **MR = price** only under perfect competition in the product market.
  > **Test Tip:** When a question asks why labour demand is downward sloping, explain diminishing marginal returns first, then show how this causes **MRPL** to fall.

### Why the labour demand curve slopes downward

The firm's labour demand curve is the **MRPL** curve. It slopes downward because as more workers are employed, the extra output from each additional worker usually falls when other factors, such as machinery or factory space, are fixed.

This is the law of diminishing marginal returns. If more workers share the same fixed quantity of capital, each extra worker has less capital to work with. Congestion, waiting time and duplication of tasks may appear. So **MPL** falls.

If **MPL** falls, then **MRPL** falls too, assuming marginal revenue does not rise enough to offset it.

In a diagram, you should describe this clearly:

- The vertical axis shows the **wage rate** or labour cost
- The horizontal axis shows the **quantity of labour**
- The firm's labour demand curve is labelled **DL = MRPL**
- The curve slopes downward from left to right

In a perfectly competitive labour market, the firm is a wage taker. This means the wage is fixed by the market for the individual firm. The wage line is horizontal.

A profit-maximising firm hires workers up to the point where:

wage = MRPL

Why? Because:

- if **MRPL > wage**, an extra worker adds more to revenue than to cost, so the firm should hire more
- if **MRPL < wage**, an extra worker adds more to cost than to revenue, so the firm should hire fewer
- profit is maximised where **wage = MRPL**
  > **Key Term: marginal productivity theory**
  > The theory that a firm's demand for labour depends on the extra revenue generated by additional workers.

This rule must be used carefully. In a competitive labour market, wage equals the marginal cost of labour. That is why the rule can be written as **wage = MRPL**. In other labour market structures, especially monopsony, the more accurate rule is **MCL = MRPL**, but that is beyond the narrow focus here.

Another key distinction is product market structure. If the firm sells output in an imperfectly competitive market, then **MR is less than price**. In that case, **MRPL** is lower than **MPL × price**. So labour demand may be lower than students expect if they wrongly use price instead of MR.

### Shifts in labour demand and how to evaluate the theory

A change in the **wage rate** causes a movement along the labour demand curve. But other factors shift the whole demand curve.

Main causes of a rise in labour demand:

- **Higher demand for the final product**  
  If consumers buy more electric cars, firms may need more engineers and assembly workers.

- **Higher labour productivity**  
  Better training, stronger management, improved technology or better infrastructure can increase **MPL**, raising **MRPL**.

- **Higher product price or marginal revenue**  
  If the firm receives more revenue from each extra unit sold, each worker becomes more valuable.

- **Higher price of substitute factors**  
  If machinery becomes more expensive, firms may switch towards labour.

Main causes of a fall in labour demand:

- Lower product demand
- Lower productivity
- Lower product price or lower MR
- Cheaper substitute capital, such as automation
- Higher non-wage labour costs, such as employer National Insurance contributions or pension costs

A useful chain for analysis is:

Higher productivity → higher MPL → higher MRPL → rightward shift in labour demand → higher employment at a given wage

Or:

Fall in product demand → lower derived demand for labour → leftward shift in labour demand → lower employment and wage pressure

> **Key Term: profit-maximising employment**
> The quantity of labour employed where the extra revenue from the last worker equals the extra cost of hiring that worker.

For evaluation, marginal productivity theory is useful but simplified.

On the one hand, it gives a clear microeconomic explanation of why firms hire workers and why productivity matters. It is especially strong in showing how labour demand links to output markets. It also explains why high-productivity workers or workers producing high-value output may be in greater demand.

On the other hand, actual labour markets are not always perfectly competitive. Wages are often influenced by trade unions, contracts, efficiency wage policies, discrimination, monopsony power, government regulation and imperfect information. In some sectors, firms may keep workers during a downturn because recruitment and training costs are high. In others, labour and capital may be complements rather than close substitutes, so a fall in capital costs may actually increase labour demand.

It also depends on time period. In the short run, firms may not adjust employment much because labour contracts are fixed. In the long run, firms have more scope to substitute labour with capital or to reorganise production.

How to structure an evaluative answer:
Start with the core theory and apply it to the context. Then weigh at least two factors that may change the outcome. For example, discuss whether the product market is competitive or imperfectly competitive, whether labour is highly skilled or easy to replace, and whether the time period is short run or long run. Use context-specific evidence such as productivity, consumer demand, labour costs or automation. End with a reasoned judgement on how far marginal productivity theory explains labour demand in that case.

> **Test Tip:** In 15- or 25-mark questions, avoid giving a pure textbook answer. Apply the theory to the industry in the question, then evaluate using market structure, productivity, time period and labour-market institutions.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- The demand for labour is a **derived demand** from demand for final goods and services
- Labour demand comes from firms, not workers
- **MPL** is the extra output from one more worker
- **MRPL** is the extra revenue from one more worker
- The formula is **MRPL = MPL × MR**
- Under perfect competition in the product market, **MR = price**, so **MRPL = MPL × price**
- The firm's labour demand curve is its **MRPL** curve
- Labour demand slopes downward because diminishing marginal returns cause **MPL** and **MRPL** to fall
- In a competitive labour market, a profit-maximising firm employs labour up to **wage = MRPL**
- A wage change causes a movement along labour demand, not a shift
- Labour demand can shift because of product demand, productivity, output price, prices of other factors and non-wage labour costs
- Marginal productivity theory is useful but limited because real labour markets are affected by market power, institutions and regulation

## Key Terms and Concepts

- derived demand
- demand for labour
- marginal physical product of labour (MPL)
- marginal revenue product of labour (MRPL)
- marginal revenue (MR)
- marginal productivity theory
- profit-maximising employment


Labour Markets - Demand for labour and marginal productivity theory