Fifteen volunteers were put on the Supper Dooper Human Kibble Diet(tm) for a month. They were weighed at the start and again after 30 days. Thus you can take `data1["start"][0]` and `data1["end"][0]` to be the weight of the same person with the first measurement at the start and the second measurement at the end of 30 days, etc. Thus, the people in "start" and the people in "end" *are* the same. The makers of The Super Dooper Human Kibble Diet(tm) are anxious to see the results of this study because they are planning to offer a money back guarantee of "Lose at least 10 Pounds in 30 days or your money back