ChainWhat it assumes · how to break it
Start
Many consumers underestimate the long-term harm of regularly drinking sugary drinks, such as tooth decay, obesity and type 2 diabetes.
1
As a result, consumers believe the benefit of sugary drinks is higher than it really is, so their perceived marginal private benefit is above the true benefit.
imperfect information · demerit good
imperfect information · demerit good
Assumes: Consumers lack information about the long-term harm.
But: Health campaigns and labelling mean many consumers know the risks; if they still choose sugary drinks, their consumption reflects their preferences.
2
Since consumers decide how much to buy by comparing their perceived benefit with the price, they buy more than they would if they were fully informed.
consumer decision-making · rational choice
consumer decision-making · rational choice
Assumes: Consumers act on the information they have.
But: Many consumers act on habit or impulse, so better information may change their choices only a little.
3
Therefore, consumption settles at Q1 where perceived MPB = MPC, beyond Q* where the true MPB = MPC.
overconsumption
overconsumption
Assumes: The information gap changes behaviour.
But: Consumers who act on habit may buy the same amount whatever information they have.
4
This means on each unit between Q* and Q1 the cost of producing it is greater than the benefit consumers really get, so welfare is lost and resources are allocatively inefficient.
welfare loss · allocative inefficiency
welfare loss · allocative inefficiency
Best link to attack
Assumes: Someone other than the consumer can judge the consumer's true benefit.
Assumes: Someone other than the consumer can judge the consumer's true benefit.
But: Deciding that consumers misjudge their own benefit is a value judgement; if the government's view of true benefit is wrong, the measured welfare loss is wrong too.
End
An information gap causes a welfare loss: consumers buy units between Q* and Q1 whose cost exceeds the benefit they really get.
Evaluation chain
- E1However, the welfare loss depends on someone being able to say what the consumer's true benefit is.
- E2Because it is the government that decides what the true benefit is, this involves a value judgement about how people should live.
- E3As a result, if that judgement is wrong, the true MPB curve is misplaced and policies such as a sugar tax may reduce welfare.
- E4So the welfare loss is clear where consumers plainly lack facts, but its size depends on whose view of benefit is used, and critics see correction as paternalism.
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Questions this answers
- Using a diagram, explain how imperfect information causes a welfare loss.
- Explain why information gaps lead to allocative inefficiency.
- Evaluate whether governments should intervene when consumers lack information.
Diagram
Perceived MPB above true MPB (= MSB), with MPC = MSC (supply): market output Q1 where perceived MPB = MPC, social optimum Q* where true MPB = MPC, so Q1 > Q*. Shade the welfare loss triangle between perceived MPB and true MPB from Q* to Q1, with its point at Q*.
Reverse and related
Consumers underestimate the benefit of a merit good → underconsumption and a welfare loss on the units between Q1 and Q*.