Studies have established that only a small percentage of reported UFOs are actual hoaxes, while the majority are observations of some real but conventional object – most commonly aircraft, balloons, or astronomical objects such as meteors or bright planets – that have been misidentified by the observer as anomalies. A small percentage of reported sightings (usually 5 %-20 %) are classified as unidentified flying objects in the strictest sense.
Certain scientists have argued that all UFO sightings, in the strictest sense, are misidentifications of prosaic natural phenomena and historically, there was debate among some scientists about whether scientific investigation was warranted given available empirical data. Very little peer-reviewed literature has been published in which scientists have proposed, studied or supported non-prosaic explanations for UFOs.
UFO reports became more common after the first widely publicized US sighting – reported by private pilot Kenneth Arnold in 1947 – that gave rise to the popular terms "flying saucer" and "flying disc". Since then, millions of people have reported that they have seen UFOs.