Background/aimIt is widely believed that 'creaky voice' ('creak', 'vocal fry', 'glottal fry') is increasingly prevalent among some English speakers, particularly among young American women. Motivated by the widespread and cross-disciplinary interest in the phenomenon, this paper offers a systematic review of peer-reviewed research (up to January 2019) on the prevalence of creaky voice in varieties of English. The review aimed to understand whose and what speech has been studied, how creaky voice prevalence has been measured, and what the findings collectively reveal. MethodLiterature was located by searching four electronic databases (ProQuest, PubMed, SCO-PUS, Web of Science) and the proceedings of two recurrent conferences ('ICPhS' and 'SST'). Studies were included if they reported the prevalence of creaky voice in naturalistic samples of English spoken by vocally-healthy speakers. Reference lists of included studies were cross-checked. ResultsOnly ten studies meeting inclusion criteria were identified. All studies sampled a small number of speakers and/or short durations of speech. Nine were recent studies of American-English speakers, and many of these sampled young, female, college students. Across the ten studies, creaky voice was detected using three types of methods, and prevalence was calculated using five different formulae. The findings show that prevalence varies across groups, individuals, and contexts. However, the precise nature of this variability remains unclear due to the scarcity and methodological heterogeneity of the research. ConclusionsThis paper illustrated the application of systematic literature review methods in sociophonetic research-a field in which such methods are not common. The review found that PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.creaky voice prevalence in English is not well understood, and that widespread claims of its recent increase among young American women have not been empirically confirmed. A number of specific limitations in the existing research are highlighted, which may serve as a guide for future research design. PLOS ONEThe prevalence of creaky voice in English PLOS ONE | https://doi.org/10.

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