Three students are conducting separate studies. John is interested in whether a psychological study on the impact of sleep on labor productivity is...

4. Three students are conducting separate studies. John is interested in whether a psychological study on the impact of sleep on labor productivity is correct. Violet is interested in finding out why people function best when sleeping 8 hours a day. Stephen is going to use statistics to attempt to resolve an issue in proving his hypothesis. What is common to all three cases?