Vocal indicators of body size in men and women: a meta-analysis

Animals often use acoustical cues, such as formant frequencies, to assess the size of potential mates and rivals. Reliable vocal cues to size may be under sexual selection. In most mammals and many other vertebrates, formants scale with vocal tract length allometrically and predict variation in size more reliably than fundamental frequency or pitch (F0). In humans, however, it is unclear from previous work how well voice parameters predict body size independently of age and sex. We conducted a meta-analysis to establish the strength of various voice–size relationships in adult men and women. We computed mean weighted correlations from 295 coefficients derived from 39 independent samples across five continents, including several novel and large cross-cultural samples from previously unpublished data. Where possible, we controlled for sample size, sample sex, mean age, geographical location, study year, speech type and measurement method, and ruled out publication bias. Eleven of 12 formant-based vocal tract length (VTL) estimates predicted men's and women's heights and weights significantly better than did F0. Individual VTL estimates explained up to 10% of the variance in height and weight, whereas F0 explained less than 2% and correlated only weakly with size within sexes. Statistically reliable size estimates from F0 required large samples of at least 618 men and 2140 women, whereas formant-based size estimates required samples of at least 99 men and 164 women. The strength of voice–size relationships varied by sample size, and in some cases sex, but was largely unaffected by other demographic and methodological variables. We confirm here that, analogous to many other vertebrates, formants provide the most reliable vocal cue to size in humans. This finding has important implications for honest signalling theory and the capacity for human listeners to estimate size from the voice.