Case study practice: plastic bags and waste

What this lesson teaches

• I can explain the causes of market failure: public goods, externalities, information failure, immobile factors and market dominance.

  Syllabus 9570, 2.3.2(b). Market Failure and its Causes: Markets may fail in terms of; non-provision of public goods due to non-rivalry and non- excludability; non-socially optimal levels of goods and services due to the presence of externalities, information failure (including asymmetric information), immobility of factors of production, and market dominance

• I can explain how taxes, subsidies, quotas, tradeable permits, provision, rules and public education correct market failure.

  Syllabus 9570, 2.3.3(b). Microeconomic Policies: Policy measures including taxes and subsidies, quotas and tradeable permits, joint and direct provision, rules and regulations, public education in achieving efficiency and equity

• I can judge how well each policy works and explain government failure.

  Syllabus 9570, 2.3.3(c). Microeconomic Policies: Effectiveness of policy measures and government failure

Make a guess

Plastic waste rises from 800 to 900 thousand tonnes, and the share recycled falls from 10% to 8%. What happens to the tonnes recycled?

1. They fall by 2 thousand tonnes, the drop in the rate.
2. They fall, from 80 to 72 thousand tonnes.
3. They rise, because there is more waste to recycle.

The extracts

Extract 1: Running out of room

Singapore burns most of the waste it cannot recycle and sends the ash to Semakau Landfill, an island south of the main island. The landfill is expected to be full by around 2035, and in a small country it is hard to find space for another one. Plastic adds to the problem. Most plastic is used once, thrown away and burnt, and only a small share is recycled. Burning it also releases carbon dioxide. Every shopper who takes a free bag adds a little to these costs, which are paid by society as a whole rather than by the shopper. Written for these notes from public information.

Extract 2: Five cents a bag

Since 3 July 2023, large supermarket operators in Singapore have had to charge at least 5 cents for each disposable carrier bag. Before then, bags were given out free. Far fewer bags are now taken, as many shoppers bring their own reusable bags (Figure 1). Not everyone is pleased. Many households used to reuse supermarket bags to line their rubbish bins, and some now buy packs of plastic bin liners instead. Smaller shops, wet markets and food stalls are not covered by the charge, so bags there are still free. Some shoppers say 5 cents is too small to matter to their budget, yet they still dislike paying for something that used to be free. Written for these notes from public information.

Extract 3: Other ways to cut plastic waste

Since April 2026, drinks sold in plastic bottles and metal cans in Singapore carry a 10-cent deposit. Shoppers pay it when they buy the drink and get it back when they return the empty container at a collection point. Germany has run a similar scheme since 2003, and most containers there are returned. Other approaches focus on information and habits. Campaigns show how long plastic lasts and how much waste each household creates. Some food delivery apps no longer include disposable cutlery unless the customer asks for it. Supporters say such nudges are cheap. Critics reply that education is slow, and that people who know the facts do not always change what they do. Written for these notes from public information.

How the 8- and 10-mark parts are marked

Data parts (1 to 3 marks)

Point-marked. A 'describe' part gives 1 mark for the overall trend and 1 for a refinement, such as when the change was fastest. An 'explain' or 'conclude' part gives marks for the evidence quoted and the reasoning that links it to the answer.

8 marks: L2 (4 to 6)

Two-sided analysis. Both the case for and the case against are explained with clear chains and tied to evidence from the extracts. A top L2 answer develops both sides fully.

8 marks: L1 (1 to 3)

One-sided, or points listed without explanation, or little use of the case.

8 marks: E (1 to 2)

E2: a reasoned judgement that answers the question in the context of the case, saying what the answer depends on. E1: a judgement that is stated but not explained.

10 marks: L2 (4 to 7)

Both policies or both sides are analysed with developed chains and case evidence. If only one of two required policies is developed, the answer is usually capped at about 5.

10 marks: L1 (1 to 3)

Mostly descriptive, one-sided, or not tied to the case.

10 marks: E (1 to 3)

E3: a well-reasoned judgement on which is better and why, using criteria such as effectiveness, cost and the cause of the problem, with a conclusion. E2: a reasoned judgement with less support. E1: an unsupported judgement.

Worked example: Describe a trend for 2 marks

Suppose a chart shows bus trips in a city as an index. The values are 100 in 2019, 40 in 2020, 60 in 2021, 85 in 2022 and 95 in 2023. The question asks you to describe the change.

1. Overall trend (1 mark): trips fell from 2019 to 2023, from 100 to 95.
2. Refinement (1 mark): they fell sharply to 40 in 2020, then rose every year after.
3. Quote the figures you use, with years.
4. Do not explain why. 'Describe' asks only what happened.

Watch out for this

When a question says 'explain what can be concluded', I copy out the figures from the table.

Figures are only the evidence. Each mark needs the evidence plus what it shows, such as 'waste rose 5% while the recycling rate fell, so the tonnes recycled fell'.

Check your understanding

In Table 1 the share of plastic waste recycled goes from 6% to 5%. How should your answer describe this change?

1. A 1 percentage point fall, about a sixth of the old 6%.
2. A fall of 1%, since 6% minus 5% leaves a gap of 1.
3. A fall of 20%, since the drop of 1 is a fifth of the new 5%.