If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

Bias in samples and surveys


A high school has a policy that students' phones must be kept away during class. A principal used the school roster to poll a random sample of 50 students, and only 10, percent said that they ever had their phone out during class. The next day, the principal observed classrooms and noticed that approximately 25, percent of students had their phone out at some point during class.
Which of these is the most concerning potential source of bias in the principal's poll?
Choose 1 answer: