When I was in high school, I meditated for the first time for two days and my grades spiked, for I made much less stupid mistakes. After that, the effect of meditation must be maintained regularly. If I didn't meditate for say three days in the last month, the grade bonus vanished quickly.

What I am trying to say is that to someone who has never meditated before, three day meditation may well have a significant impact. However if they do not do it long term, those effects may be temporary.

well that's just what the paper tested for and had a statistically significant result. it's not nearly like 5-year clinical trials, but it's much better than nothing surely.