A researcher is designing an experiment to determine whether the production of amylase increases when a person anticipates eating starchy food. She measures the amount of amylase in the saliva of 10 volunteers who are offered a bowl of pasta and of 10 other volunteers who are offered a bowl of scrambled eggs. In analyzing her data, she finds some variation in the amount of amylase among the samples within each group, but no significant difference in the amount of amylase between the two groups. She concludes that she needs to revise her experimental design and try her experiment again. What would be the best thing she could do to improve her experiment?