Materials:
Timer
Pencil
Paper..

Procedure:
Form three groups of 10 people.
For group A, pull one out each one at a time and tell them to hold their breath. Make sure to say "Hold your breath for as long as you can". Record results.
For group B, do the same thing as A except tell them the average time other users got was 30 seconds. Record results.
For group C, do the same thing as B except the average time is now 1 minute. Record results.