Many people claim that they have been abducted by aliens. But, however real the experience might have seemed, it is the product of dreaming caused by sleep paralysis. In such sleep, the dreamer might hear strange noises, see flashing lights or stars, and sense shaking and juddering. Some dreamers also feel that they are being turned in their beds. All of these experiences match those of people reporting supposed abdudion by aliens. This type of sleep phenomenon is fairly common, being experienced by three out of ten people. In that sleep paralysis explains the sensations reported by everyone who claims to have been abducted by aliens, we can conclude that aliens have not come to Earth and abducted people. Which of the following is an underlying assumption of the argument above?