A drug manufacturer is testing a new headache drug. They recruit 100 subjects with headaches and have them rate the severity of their headaches on a scale of 1 to 10. The researchers randomly assign 50 of them to receive the new drug and 50 to receive a placebo. One researcher is told she will work with those that received the new drug and another researcher will work with those that received the placebo. Through an interview process each researcher determines if there has been a substantial reduction in the severity of the headache of each subject after one hour. They find that 60% of the subjects had substantial reduction in the severity of their headaches in the treatment group compared to only 30% in the control group. What fundamental component is missing in this experimental design?