A ward office plans to put a community compost bin at the end of every lane so that households will drop their kitchen waste there instead of adding it to the general rubbish, which would cut the load carried to the town dump. Which of the following, if true, gives the strongest reason to doubt that the plan will achieve its purpose?

The plan succeeds only if households actually change where they put the waste. Evidence that, wherever the scheme has been tried, people kept using the nearer container strikes exactly at that link and leaves the new bins empty. The purchase cost bears on what the scheme is worth, not on whether it works; the material of the bins and the speed of decomposition touch the household's choice not at all.