A scientist was conducting an experiment involving two brands of toothpaste. He randomly selected two groups of 15 children. He wanted to see which brand of toothpaste prevented the most cavities. All of the children were given detailed directions describing when and how they should brush their teeth. After six months the children were taken to the same dentist and the number of cavities each child had was recorded. This data was used to determine which toothpaste is more effective.

Explain how replication is used in this experiment.