Professor Villanueva Has Developed a New Form of Therapy That

Professor Villanueva has developed a new form of therapy that he believes reduces anxiety. He bases his claim on the fact that 63 percent of the people who go through his program show little to no anxiety after treatment. Why might a scientist be skeptical of his claim?

A) There is no control group to compare to the people in his program.
B) He lacks a well-developed hypothesis.
C) Over 30 percent of the people did not improve.
D) The professor conducted an experiment when he should have done a laboratory observation.