Arandomized, double-blind experiment studied whether magnetic fields applied over a painful area can reduce pain intensity. the subjects were 50 volunteers with postpolio syndrome who reported muscular or arthritic pain. the pain level when pressing a painful area was graded subjectively on a scale from 0 to 10 (0 is no pain, 10 is maximum pain). patients were randomly assigned to wear either a magnetic device or a placebo device over the painful area for 45 minutes. all patients rated their pain before and after application of the device. for the 29 patients assigned to the magnetic group, the mean pain scores before and after treatment were 9.6 and 4.4, respectively. explain briefly why a matched pairs procedure must be used to assess whether application of the magnetic device significantly lowers pain. because we do not know the population standard deviation or the population mean. because we do not know whether the population is normal. because there are two groups - placebo and treatment. because we have 2 measurements, before and after, for each patient. the 21 patients assigned to the placebo device had mean pain scores before and after treatment of 9.5 and 8.4, respectively. explain briefly why we cannot use a matched pairs procedure to test the hypothesis that the magnetic device is significantly better than the placebo at reducing pain intensity in patients with postpolio syndrome.