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A state implements a worker training program in Year 2, affecting only firms in the treatment county. Mean worker productivity (output per worker) is:

| Year | Treatment County | Control County | |------|-----------------|----------------| | Year 1 | 80 | 82 | | Year 2 | 84 | 83 | | Year 3 | 88 | 86 |

Assuming parallel trends (both counties would move together absent the program), the difference-in-differences estimate of the Year 2 treatment effect is: