Government intervention in the price mechanism – Price Mechanism (Senior 4 Economics) | Ganzaa

Price Mechanism

Lessons

Senior 4 · Economics

Price Mechanism

4 lessons

Lesson 2 of 4

Government intervention in the price mechanism

30 min

3.5 million farmers, one subsidy system

In the fiscal year 2024–25, the Ministry of Agriculture and Animal Resources (MINAGRI) reports that subsidised seeds and fertilisers reached more than 3.5 million farmers through the Smart Nkunganire System, and 110,691.2 tonnes of fertiliser were distributed. Presenting the 2026–27 budget, the Minister of Finance said the government had "prioritized agriculture inputs and irrigation" (MINECOFIN). In the same economy the RRA levies excise duty on beer, cigarettes and fuel, RURA caps the pump price of petrol, and a law bans plastic carry bags. Rwanda relies on the price mechanism, but it does not leave it alone. This lesson asks why governments intervene, what tools they use, and what can go wrong.

1. Why governments intervene

Reason	The market's failure	Rwandan example of a response
Public goods	Not supplied, because non-payers cannot be excluded	Roads, street lighting and security paid from the budget
Merit goods	Under-consumed (education, health care, nutrition)	Public schools and the School Feeding Programme
Demerit goods	Over-consumed (alcohol, tobacco)	Excise duties on beer and cigarettes (RRA)
Externalities	Social costs and benefits are ignored	Law N° 17 of 2019 banning plastic carry bags
Inequality	"For whom" depends on income	Social protection; subsidised inputs for small farmers
Price instability	Farm prices swing with harvests	The National Strategic Grain Reserve (Lesson 3)
Monopoly	High prices and low output	Regulation of utilities by RURA
Strategic goals	The market may neglect long-term goals	Support for irrigation, exports and new industries

Definition

Indirect tax: a tax on spending on goods and services, collected from sellers. A specific tax is a fixed sum per unit (Frw 183 per litre of petrol); an ad valorem tax is a percentage of the price or value (65% on most beer).

Subsidy: a payment by the government to producers (or consumers) that lowers the cost of producing or buying a good, such as subsidised fertiliser.

2. The tools of intervention

Indirect taxes shift supply up (left): price rises, quantity falls, the state gains revenue. Used for demerit goods and goods with negative externalities.
Subsidies shift supply down (right): price falls, quantity rises. Used for merit goods, farm inputs and infant industries.
Price controls: maximum and minimum prices (Lesson 4).
Direct provision of public and merit goods: roads, schools, health centres.
Regulation and legislation: bans, quality standards, licences, zoning, minimum ages.
State enterprises in key sectors.
Buffer stocks and stabilisation funds (Lesson 3).
Information: health campaigns, labelling, market price information for farmers.
Redistribution: progressive income taxes and transfers to poor households.

Worked example 1: a subsidy on tomatoes (illustrative)

The tomato market of Unit 2 has $Q_d = 1\,600 - 2P$ and $Q_{s} = - 200 + 4 P$ , with equilibrium at Frw 300 and 1,000 kg a day. The government pays sellers Frw 60 per kg. Sellers now receive $P + 60$ , so

Q_{s} = - 200 + 4 (P + 60) = 40 + 4 P

1\,600 - 2P = 40 + 4P \Rightarrow 6P = 1\,560 \Rightarrow P = 260,\ Q = 1\,600 - 520 = 1\,080

	Before	After	Change
Price paid by buyers	Frw 300	Frw 260	Buyers gain Frw 40 per kg
Price received by sellers	Frw 300	$260 + 60 = \text{Frw } 320$	Sellers gain Frw 20 per kg
Quantity	1,000 kg	1,080 kg	+80 kg

Cost to the government: $60 \times 1\,080 = \text{Frw } 64\,800$ a day. Buyers get two-thirds of the benefit because, at the old equilibrium, supply is more elastic than demand (PES = 1.2, |PED| = 0.6, and $\frac{1.2}{1.2 + 0.6} = \frac{2}{3}$ ).

Worked example 2: specific or ad valorem?

Compare RRA's two forms of excise on two illustrative products.

Ad valorem: beer that is not mainly local pays 65% of its factory price. On a bottle with a factory price of Frw 600, the duty is $0.65 \times 600 = \text{Frw } 390$ ; if the factory price rises to Frw 800, the duty rises to $0.65 \times 800 = \text{Frw } 520$ .
Specific: premium petrol pays Frw 183 per litre, whatever its price.

Analysis: ad valorem revenue rises automatically with prices (useful during inflation), while a specific tax keeps the same franc amount, so its real value falls as prices rise unless it is revised.

3. Government failure

Intervention can also go wrong. Government failure occurs when intervention makes the allocation of resources worse rather than better. Causes include: poor information about costs and benefits; high administrative costs; unintended consequences, such as smuggling when taxes are high; subsidies that reach people who did not need them; delays and red tape; political pressure; and corruption. A good policy answer weighs the market failure against the risk of government failure.

Warning

Do not shift demand for a tax or subsidy on producers. A tax or subsidy paid to or by sellers changes their costs, so it shifts the supply curve. The demand curve stays where it is; buyers simply move along it to the new price.

Tip

For any intervention, answer four questions: What market failure does it fix? Which curve moves, and how? Who gains and who pays? What could go wrong?

Important

Discuss. Is subsidising fertiliser for millions of small farmers a good use of public money? Consider who gains, the cost to the budget, the effect on food prices, and the risk of government failure.

EconplusDal, "Indirect Tax - Full Market Impact". Watch how a tax changes the price paid, the price received, the quantity and the government's revenue; a subsidy works in the opposite direction, as in Worked example 1.

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Practice

Give five reasons why the Government of Rwanda intervenes in the price mechanism.
Distinguish between a specific tax and an ad valorem tax, with a diagram of each.
Demand is $Q_{d} = 100 - P$ and supply is $Q_{s} = P - 20$ . Find the equilibrium. A subsidy of 10 per unit is paid to sellers. Find the new price paid by buyers, the price received by sellers and the cost of the subsidy.
A specific tax of Frw 50 per unit is placed on a good with perfectly inelastic demand. Who bears the tax? Explain with a diagram.
A bottle of beer has a factory price of Frw 700. Calculate the excise duty at 65% and at 40%.
Explain three methods, other than taxes and subsidies, that governments use to influence markets.
Explain the meaning of government failure and give three causes.
"Government intervention always improves on the free market." Discuss.

Show answersHide answers

Any five: public goods, merit goods, demerit goods, externalities, inequality, price instability, monopoly, strategic goals.
Specific: a fixed sum per unit, a parallel upward shift of supply. Ad valorem: a percentage of price, a shift that widens as price rises.
Before: $100 - P = P - 20 \Rightarrow P = 60,\ Q = 40$ . After: $Q_{s} = (P + 10) - 20 = P - 10$ : $100 - P = P - 10 \Rightarrow P = 55,\ Q = 45$ . Buyers pay 55; sellers receive 65; cost $= 10 \times 45 = 450$ .
Buyers bear all of it: quantity does not change, so the price rises by the full Frw 50.
$0.65 \times 700 = \text{Frw } 455$ ; $0.40 \times 700 = \text{Frw } 280$ .
Any three: price controls; direct provision; regulation and legislation (such as the plastic-bag ban); buffer stocks; state enterprises; information campaigns; redistribution.
Intervention that makes resource allocation worse. Causes: poor information, administrative costs, unintended consequences, political pressure, corruption.
Intervention can correct market failures (public goods, externalities, inequality), but it can also fail. Whether it improves on the market depends on the size of the market failure, the quality of the policy and the government's information. Judge each case on evidence.

Quick check

A subsidy of Frw 60 per kg is paid to tomato sellers. Which curve moves, and which way?

Key points

Governments intervene because of public goods, merit and demerit goods, externalities, inequality, instability, monopoly and strategic goals.
Tools include indirect taxes (specific or ad valorem), subsidies, price controls, direct provision, regulation, state firms, buffer stocks, information and redistribution.
A subsidy shifts supply down; buyers and sellers share the gain according to elasticities.
Intervention can fail too: weigh market failure against government failure.

Sources and credits

Input subsidies and fertiliser: Annual Report 2024–2025, Ministry of Agriculture and Animal Resources (MINAGRI).
Budget priorities: Minister Murangwa presents Frw 7,796 billion budget for 2026–27, MINECOFIN, 11 June 2026.
Excise duty rates: Declare your excise duty, Rwanda Revenue Authority (RRA).
Plastics law: Law N° 17 of 2019, via RwandaLII.
Video: Y1 16) Indirect Tax - Full Market Impact, EconplusDal, embedded from YouTube.

Written by Ganzaa: the text, the subsidy and tax diagrams (the subsidy drawn to scale from its equations), the tables, the worked examples and the practice items. The tomato market and the beer factory prices are illustrative.

13.5 million farmers, one subsidy system

21. Why governments intervene

32. The tools of intervention

43. Government failure

3.5 million farmers, one subsidy system

1. Why governments intervene

2. The tools of intervention

3. Government failure