Half of the subjects in an experiment-the experimental group-consumed large quantities of a popular artificial sweetener. Afterward, this group showed lower cognitive abilities than did the other half of the subjects-the control group who did not consume the sweetener. The detrimental effects were attributed to an amino acid that is one of the sweetener' s principal constituents.
The statement "The two groups of subjects were evenly matched with regard to cognitive abilities prior to the experiment" would best support the conclusion that some ingredient of the sweetener was responsible for the experimental results.