Historically, research on improvisation has been related to the discovery of non-Western musics, folk music, and jazz, and has depended on the development of recording techniques for its principal kinds of data. The concept of improvisation is not unitary, but includes many vastly different kinds of un-notated music-making, which casts some doubt on the efficacy of the term itself. In the history of Western art music, improvisation was originally ignored or seen as craft rather than art, but since ca. 1980 it has occupied increased attention. The association of improvisation with oral transmission has sometimes been misunderstood. The most successful standard research study has been the comparison of performances based on a single model, for example, raga in India, maqam and dastgah in the Middle East, or a series of chord changes or a tune in jazz. Improvisation as a concept—for example, as a metaphor of freedom—has been important in recent research.