A cognitive psychologist was interested in the relationship between nightly sleep duration and complex problem-solving speed. He conducted a correlational analysis to investigate this using a self-selected sample of 50 university students.
Each participant tracked their sleep for five consecutive nights using a wearable sleep tracker to calculate their average nightly sleep duration. Their problem-solving speed was then assessed in a laboratory by timing how long (in seconds) they took to complete a set of 15 advanced spatial logic puzzles.
Describe one weakness of using a self-selected sample in this study.
