That database served as an ideal social laboratory for Christakis and Fowler, who questioned each participant and his or her friends and family about their emotional state three times over 20 years.

• 这些记录对克莱斯塔基斯和福勒来说是完美的社会实验室，在过去的20年中，他们共三次询问了参与者及其家属和朋友的情绪状态。