Adult standards (also sometimes known as the nostalgia format) is aimed at "mature" adults, meaning mainly those people over 50 years of age, but it is mostly targeted for senior citizens. It is primarily on AM because market research reveals that only persons in that age group listen to music on AM in sizable numbers. Adult standards first became a popular format in the late 1970s and early 1980s as a way to reach mature adults who came of age before the rock era but were perhaps too mature for adult contemporary radio or too young for beautiful music or MOR stations. A typical adult standards playlist includes traditional pop music by artists such as Frank Sinatra and Tony Bennett, some easy listening numbers from Roger Whittaker and others, and softer tunes from the oldies and adult contemporary formats; as originally conceived, the format also features big band music, particularly from the 1940s and 1950s, though most modern stations eschew that genre. Younger artists who record in the big-band era style, such as Harry Connick, Jr., or Diana Krall, may be played as well. The term "standards" in the format's title is a reference to the standard, a song that is covered extensively by many artists over a prolonged period of time; adult standards may play true standards but are not limited to them.