Style variability in disfluency analysis for forensic speaker comparison


  • Lauren Harrington University of York
  • Richard Rhodes Universityof York/J. P. French Associates
  • Vincent Hughes University of York



disfluencies, disfluency analysis, TOFFA, forensic speaker comparison, speaking styles


Disfluencies are a natural part of speech, often going unnoticed by both speaker and listener. Recent research on disfluency profiles (McDougall and Duckworth 2017, 2018) shows that they contain speaker-specific information which could be analysed and compared in forensic speaker comparison (FSC) casework. Since samples in FSC tend to be mismatched for speaking situation and style, the present study investigates the consistency of speakers’ disfluency production across three forensically relevant tasks: a mock police interview, a paired conversation and a voicemail message. Disfluency production was found to differ significantly across tasks; in some cases, extreme within-speaker variation was observed. The results demonstrate that a speaker’s disfluency behaviour is unlikely to remain consistent across different situations. However, it was found that some individuals who demonstrated unusual production of a particular type of disfluency showed relatively consistent production of that type across all three tasks. Consequently, we recommend that disfluency analysis is not used in FSC where there are marked differences in speaking style or situation, unless distinctive disfluency production is observed in a sample.

Author Biographies

Lauren Harrington, University of York

Lauren Harrington is a PhD student at the University of York, UK. Her doctoral research focuses on the transcription of forensic audio recordings and the effect of regional accent on transcription performance in both humans and machines. Her research is funded by the White Rose College of the Arts & Humanities (supported by the AHRC). She holds a BA (Hons) in French and Linguistics and an MSc in Forensic Speech Science, and carried out research on disfluency phenomena for her MSc dissertation. She is a research assistant on the project ‘Evaluating human and automated transcripts of speech recordings: implications for forensic linguistics’ for Aston Institute for Forensic Linguistics.

Richard Rhodes, Universityof York/J. P. French Associates

Richard Rhodes is a senior forensic consultant at J. P. French Associates, a Forensic Speech and Acoustics Laboratory in York, UK. He acts as an expert witness in (mainly) criminal proceedings in court and produces reports concerning speaker comparison, transcription, questioned content analysis and other types of forensic phonetic casework. He is also Associate Lecturer in the Department of Language and Linguistic Science at the University of York where he teaches and supervises research.

Vincent Hughes, University of York

Vincent Hughes is Lecturer in Forensic Speech Science at the University of York, UK. His research interests lie in forensic speech science, phonetics, phonology, sociophonetics and sociolinguistics. His current research focuses on understanding the bases and limitations of individual speaker characterisation and the relative contribution of acoustic, auditory and biological information. He is also interested in the application of the numerical likelihood ratio framework to the evaluation of speech evidence in forensic voice comparison cases. His doctoral research considered how the definition of the relevant population with regard to regional and social dimensions of variability and sample size affects the numerical estimation of the strength of evidence.


Bates, D., Mächler, M., Bolker, B. and Walker, S. (2015) Fitting linear mixed-effects models using ‘lme4’. Journal of Statistical Software 67(1): 1–48. DOI:

Bello, R. (2006) Causes and paralinguistic correlates of interpersonal equivocation. Journal of Pragmatics 38(9): 1430–1441. DOI:

Boersma, P. and Weenink, D. (2021) Praat: Doing phonetics by computer [computer program].

Bortfeld, H., Leon, S. D., Bloom, J. E., Schober, M. F. and Brennan, S. E. (2001) Disfluency rates in conversation: effects of age, relationship, topic, role, and gender. Language and Speech 44(2): 123–147. DOI:

Branigan, H., Lickley, R. and McKelvie, D. (1999) Non-linguistic influences on rates of disfluency in spontaneous speech. In J. J. Ohala, Y. Hasegawa, M. Ohala, D. Granville and A. C. Bailey (eds) Proceedings of the 14th International Congress of Phonetic Sciences 387–390. San Francisco.

Broen, P. A. and Siegel, G. M. (1972) Variations in normal speech disfluencies. Language and Speech 15(3): 219–231. DOI:

Forensic Science Regulator (2021) Forensic science providers: codes of practice and conduct for forensic science providers and practitioners in the criminal justice system, issue 7.

Gold, E., Ross, S. and Earnshaw, K. (2018) The ‘West Yorkshire Regional English Database’: investigations into the generalizability of reference populations for forensic speaker comparison casework. In Proceedings of Interspeech 2018 2748–2752. Hyderabad. DOI:

Kasl, S. V. and Mahl, G. F. (1965) Relationship of disturbances and hesitations in spontaneous speech to anxiety. Journal of Personality and Social Psychology 1(5): 425–433. DOI:

Koumpis, K. and Renals, S. (2000) Transcription and summarization of voicemail speech. In Proceedings of Sixth International Conference on Spoken Language Processing 2000 688–691. Beijing.

Kuznetsova, A., Brockhoff, P. B. and Christensen, R. H. B. (2017) lmerTest package: tests in linear mixed effects models. Journal of Statistical Software 82(13): 1–26. DOI:

Lickley, R. J. (2001) Dialogue moves and disfluency rates. In ISCA Tutorial and Research Workshop (ITRW) on Disfluency in Spontaneous Speech 93–96. Edinburgh.

Maclay, H. and Osgood, C. E. (1959) Hesitation phenomena in spontaneous English speech. Word 15(1): 19–44. DOI:

Mahl, G. F. (1956) Disturbances and silences in the patient’s speech in psychotherapy. Journal of Abnormal and Social Psychology 53(1): 1–15. DOI:

McDougall, K. and Duckworth, M. (2017) Profiling fluency: an analysis of individual variation in disfluencies in adult males. Speech Communication 95: 16–27. DOI:

McDougall, K. and Duckworth, M. (2018) Individual patterns of disfluency across speaking styles: a forensic phonetic investigation of Standard Southern British English. International Journal of Speech, Language and the Law 25(2): 205–230. DOI:

McDougall, K., Rhodes, R., Duckworth, M., French, J. P. and Kirchhübel, C. (2019) Application of the ‘TOFFA’ framework to the analysis of disfluencies in forensic phonetic casework. In S. Calhoun, P. Escudero, M. Tabain and P. Warren (eds) Proceedings of the 18th International Congress of Phonetic Sciences 731–735. Melbourne.

Moniz, H., Batista, F., Mata, A. I. and Trancoso, I. (2014) Speaking style effects in the production of disfluencies. Speech Communication 65: 20–35. DOI:

Nolan, F., McDougall, K., de Jong, G. and Hudson, T. (2009) The DyViS database: style-controlled recordings of 100 homogeneous speakers for forensic phonetic research. International Journal of Speech, Language and the Law 16(1): 31–57. DOI:

Oviatt, S. (1995) Predicting spoken disfluencies during human–computer interaction. Computer Speech and Language 9(1): 19–36. DOI:

Padmanabhan, M., Eide, E., Ramabhadran, B., Ramaswamy, G and Bahl, L. R. (1998) Speech recognition performance on a voicemail transcription task. In Proceedings of the 1998 IEEE International Conference on Acoustics, Speech and Signal Processing 913–916. Seattle. DOI:

Siegman, A. W. and Pope, B. (1965) Effects of question specificity and anxiety-producing messages on verbal fluency in the initial interview. Journal of Personality and Social Psychology 2(4): 522–530. DOI:



How to Cite

Harrington, L. ., Rhodes, R. ., & Hughes, V. . (2021). Style variability in disfluency analysis for forensic speaker comparison. International Journal of Speech, Language and the Law, 28(1), 31–58.