Once the author started taking pills independently of their stress level, the variance of differences diminished a lot. I'd wager this supports the mean reversion hypothesis.
Also, while I agree with their general conclusion that theanine probably doesn't reduce stress, I'd give assign more probability to the hypothesis that theanine does work, but in other design settings. For example: drinking tea instead of taking pills, or measuring stress levels after a day instead of an hour, or evaluating the difference across time instead of in time chunks.
Once the author started taking pills independently of their stress level, the variance of differences diminished a lot. I'd wager this supports the mean reversion hypothesis.
Also, while I agree with their general conclusion that theanine probably doesn't reduce stress, I'd give assign more probability to the hypothesis that theanine does work, but in other design settings. For example: drinking tea instead of taking pills, or measuring stress levels after a day instead of an hour, or evaluating the difference across time instead of in time chunks.