. . Determine whether each of the following studies described is observational or an experiment. If the study is an experiment, identify the control and treatment groups, and discuss whether single- or double-blinding is necessary. If the study is observational, state whether it is a retrospective study, and if so, identify the cases and controls. 38. In a study of the effects of magnets on back pain, some sub- jects were treated with magnets while others were given non- magnetic devices With a similar appearance (Journal of the American Medical Association). (The magnets did not appear to be effective in treating back pain.)