To test a new medicine, each of 300 volunteers was assigned a distinct number from 1 to 300. Next, a calculator was used to simulate drawing 150 balls from among 300 congruent balls. The balls were numbered the same way as the volunteers so that 150 volunteers to receive the new medication would be chosen without bais. THe other volunteers received a placebo. Weeks later, the 2 group were compared. Which of the following phrases best bescribes the company's testing?