In psychology, the prevalence effect is the phenomenon that one is more likely to miss (or fail to detect) a target with a low prevalence (or frequency) than a target with a high prevalence or frequency. A real-world application of this phenomenon occurs in airport security screening; since a very small proportion of those going through security checkpoints carry weapons, security staff may fail to detect those attempting to carry weapons onto a plane. In visual perception, target prevalence describes the salience (or visibility) of an object or objects in the environment and influences visual search.An experiment similar to an x-ray baggage search at an airport reveals how likely one is to make errors when searching for low-prevalence targets. A 50-percent prevalence produced a seven-percent error rate, typical for laboratory search tasks of this sort; a 10-percent prevalence produced a 16-percent error rate, and prevalence under one percent produced a 30-percent error rate. Humans normally search for common things, such as a favorite jelly-bean flavor in a collection of flavors. When they look for rare things (such as a jelly bean in a bag of lollipops), they are likely to abandon the search quickly because the probability of success and the stakes are low. Some searches combine low prevalence with high stakes; medical screenings such as mammography or cytopathology, is an important search for a target rarely present (typically under one percent). Missing a rare target, such as a weapon smuggled onto an airplane, may have serious consequences.