We took 1,300 randomly selected undergraduates, we had them nominate their friends, and we followed both the random students and their friends daily in time to see whether or not they had the flu epidemic.
ランダムに選出した学部生1300人に 友人を挙げてもらい そのランダムの学生と友人の両方を 毎日 追跡調査して 流行のインフルエンザへの感染を調べました