Intro to Stats: Videos & Practice Problems

A sleep study recruited $120$ volunteers and assigned each volunteer to try $2$ different pillow types in random order over $2$ nights. On night one, a participant used either a memory-foam pillow or a latex pillow, and their total sleep time was recorded. On night two, they used the other pillow, and sleep time was recorded again. The study reports that overall sleep time was longer with the memory-foam pillow. Who are the subjects?