Twelve people are in a study to compare two methods of caffeine use--caffeine pills and coffee use. Each of the 1 are randomly chosen to use either the caffeine pills or drink the coffee. Then each person switches and takes either the pills or the coffee the next night. Periods of wakefulness are recorded each night. What is the explanatory variable and response variable for this study. Is there any carry over effect or dependent samples in this study? I am leaning toward a randomized experiment in this example, but it coudl also be observational because we are just observing how awake they are with the caffeine!.