Researchers are testing an experimental drug believed to be effective for controlling mild symptoms of arthritis. They are concerned that this population is older, likely to have additional health problems, and taking additional medications. Therefore, there is the possibility that there could be many confounding variables when comparing two different groups. The researchers decide to conduct a "before-after" type trial where they will compare the same test group's experiences for a period when they receive the test drug versus their experiences when they do not receive the test drug. What type of design is this? Placebo-controlled Active comparator Cross-over Add-on