Exercise 1 solution

Arithmetic first. The cost per young person is 90,000 divided by 450, which is 200. The fall in reported offences is 120 minus 96 = 24, and 24 divided by 120 is 0.20, so the councillor's 20% is arithmetically right (computed in Python).

The claim, though, is that the club caused the fall. A good answer picks at least three ideas from earlier chapters and says what each would require.

- Correlation and cause (Chapter 10): the figures show two things happening in the same year, not that one produced the other. Reverse causation, a third variable (for example a change in policing or a new housing estate) and coincidence all remain possible. You would want to know whether similar towns without a club saw similar falls.
- Dark figure of crime (Chapter 9): "reported" offences are not all offences. If recording practices or willingness to report changed, the 20% could be a change in counting, not in behaviour.
- Differential association (Chapter 9): the theory says criminal behaviour is learned in close personal groups. If the club moved young people into different peer groups, that would be a plausible mechanism, but you would need evidence about who attended, not just how many.
- Selection bias (Chapter 10) and groups (Chapter 5): young people who choose to go to a club may already be the ones least likely to offend. The 450 users are not a random sample of the town's young people.
- Labelling (Chapter 9): a change in how the police or school record or label young people could shift the numbers without a change in what they do.

A strong answer ends by saying what evidence would settle it: offence rates among users and non-users before and after, comparison towns, and unchanged recording rules. A weaker answer accepts the 20% as proof or rejects the claim without saying why. Anything about how clubs work in general that is not from the course should be marked "(check".