People with anxiety disorders are selected to participate in a study on a new drug for the treatment of this disorder. The researchers know that the drug is effective in treating the disorder, but they are concerned with possible side effects. In particular, they are concerned with the effects of the drug on cognitive abilities. Therefore, they ask each participant in the experiment to identify a family member or friend who is the same gender as the participant and who is of a similar age as the participant (within 5 years) but who does not have an anxiety disorder. The researchers then administer the drug to those with the disorder and measure cognitive functioning in both groups. What type of design is this? Would you suggest measuring cognitive functioning more than once? When and why?