The development of a valid and reliable instrument to grade the difficulty of vocal solo repertoire
The purpose of this study is to design a valid and reliable instrument, the Ralston Repertoire Difficulty Index (RRDI), to measure the difficulty of solo vocal repertoire. Another important aspect of this instrument is its ability to be used by all voice teachers, regardless of their level of experience in teaching in private voice studios. The instrument also was examined for its ability to discriminate among songs by categorizing repertoire into different difficulty levels. Seven criteria were selected and defined to represent the technical characteristics that contribute to the difficulty of vocal solo repertoire. A measurement instrument incorporating these characteristics was designed to evaluate each characteristic individually.