All had previously averaged between seven and eight hours of sleep per night, but for the study they were now divided into four groups. Members of three groups were allowed to sleep for eight hours, six hours, or four hours a night.
Kõik nad olid varem maganud öösel 7 – 8 tundi, kuid uurimise ajal jagati nad nelja gruppi: kolmel grupil lasti öösel magada kaheksa, kuus ja neli tundi ning neljandal grupil ei lastud kolme ööpäeva jooksul üldse magada.