Kara works as a dog trainer. she reads a new book that describes some unusual training methods, and she wants to test them out on the dogs she works with. she assigns each dog to one of two groups by picking a number out of a hat. half the dogs are assigned to one group, and half the dogs are assigned to the other group. for a month, she trains one group using her old methods and the other group using the unusual methods. at the end of the month, kara records that the dogs that were trained with her old methods obey her 80 percent of the time and those that were trained with the unique methods obey her 90 percent of the time. kara concludes that the unique methods work better. kara can best improve her experimental design by: