Deconstructing the nPVI: A Methodological Critique of the Normalized Pairwise Variability Index as Applied to Music

The normalized pairwise variability index (nPVI) is a measure originally used to compare the rhythms of languages. Patel and Daniele (2003a) introduced the nPVI to music research and it has since been used in a number of studies. In this paper, I present a methodological criticism of the nPVI as applied to music. I discuss the known qualitative features of the nPVI and illustrate the nPVI's fundamental features and assumptions through its application to a number of musical datasets. My principle criticism regards the application of a linear average (the nPVI) to categorical data (rhythmic notation). I argue that that simpler mathematical characterizations, which are more musically intuitive, can capture the same useful information as the nPVI. Specifically, counting the proportion of successive IOIs that are identical accounts for as much as 98% of variation in nPVIs in musical corpora. I argue that abstract mathematical measures ought to be avoided in preference for more concrete empirical descriptions of specific rhythmic features, and that, rather than focusing on a single measure, multiple measures ought to be used. Finally, I conclude that the usage of nPVI in music research should be limited to specific methodologically justified contexts.