While scratching is most associated with hip hop music, where it emerged in the mid-1970s, from the 1990s it has been used in some styles of rap rock, rap metal and nu metal. In hip hop culture, scratching is one of the measures of a DJ's skills. DJs compete in scratching competitions at the DMC World DJ Championship and IDA (International DJ Association, formerly known as ITF (International Turntablist Federation). At scratching competitions, DJs can use only scratch-oriented gear (turntables, DJ mixer, digital vinyl systems or vinyl records only). In recorded hip hop songs, scratched "hooks" often use portions of other songs.