Reducing unemployment.
Problem: Will cash bonuses speed the return to work of unemployed people? A state department of labor notes that last year 68% of people who filed claims for unemployment insurance found a new job within 15 weeks. As an experiment, the state offers $500 to people filing unemployment claims if they find a job within 15 weeks. The percent who do so increases to 77%.
Required:
Suggest some conditions that might make it easier or harder to find a job this year as opposed to last year. Confounding with these lurking variables makes it impossible to say whether the bonus really caused the increase.