A hand sanitizer was advertised to be more effective at killing bacteria than any
antibacterial soap. Students were split evenly into 4 groups to test this claim.
Groups 1-3 washed their hands using the assigned hand sanitizer or soap and
warm water for two minutes, and then dried their hands with a paper towel.
Group 4 rubbed their hands vigorously for 2 minutes in warm water, without any
soap or sanitizer, and then dried their hands with a paper towel. After washing,
each student's hands were swabbed and the swab was applied to a culture plate
and incubated. Finally, the bacterial cultures were counted.
What are 3 constants of this experiment?