1. Lenth, Russell. 2018. emmeans: Estimated marginal means, aka least-squares means. R package version 1.1.3.
2. Boersma, Paul & Weenink, David . 2017. Praat: Doing phonetics by computer (computer program); version 6.0.28. http://www.praat.org/ (accessed 20 March 2017).
3. Becker-Kristal, Roy . 2010. Acoustic typology of vowel inventories and Dispersion Theory: Insights from a large cross-linguistic corpus. Ph.D. dissertation, UCLA.