To study the effects of a medication on migraines, every 10th adult from an alphabetized list of patients who suffer from migraines were selected. Then, the sample was surveyed about the number of migraines they have each month. The names of the 50 adults selected were written on equal sized tiles, placed in a bag, and mixed well. The people with names on the first 25 tiles selected were given the migraine medication. The remaining 25 people were given a placebo. After six months, all patients were surveyed again about the number of migraines they had each month. The change in the mean number of migraines between the two groups was compared. Which of the following is the best description of the randomization approach? random selection random assignment both random selection and random assignment neither random selection nor random assignment