Apreliminary study conducted at a medical center in st. louis has shown that treatment with small, lowintensity magnets reduces the self-reported level of pain in polio patients. during each session, a patient rested on an examining table in the doctor's office while the magnets, embedded in soft pads, were strapped to the body at the site of pain. sessions continued for several weeks, after which pain reduction was measured.

Answer: this experiment uses men with herniated discs and men without herniated discsto test if a treatment will have a certain effect we always need to have a group control. that group control should have the same size as the group that's going to take the treatment. another important thing  that makes a group control is having them not take any treatment, or in other words make them take a placebo. lastly, the control group should be representative of the same population, men,  to serve as comparison to the treatment group.

Dcalifornia they have the most people with 200+ people per square mile