Describe the replicated interrupted time-series design that assessed the effectiveness of New York's bottle return law. Why can we use it to form a tentative causal link between the law and the reduction in some litter?

Question

What will be an ideal response?

Answer 1

The replicated interrupted time-series design monitored the amount of returnable and nonreturnable litter before and after New York mandated that soft drink and beer bottles have a deposit that is refunded on return. The investigators looked at the amount of litter in New York City and in nearby New Jersey, which didn't have such a law.
The results indicated that people removed the litter for which they could get a monetary refund in New York; the same kind of litter was left on the ground in New Jersey. In both states, the amount of litter that was nonrefundable remained unchanged.
This procedure allows for some assessment of causation because you would expect both New York and New Jersey to have comparable litter if the bottle return law had been ineffective. In New York, with the law, there was less litter. The researchers also looked at the trend over time. They discovered that the pattern was consistent with the bottle return law as actually leading to less litter.