It is interesting to compare the hand spans of pianists with non-pianists. In other words, do pianists’ hands reflect the human population as a whole?
Much of the detailed published anthropometrical data are not based on random samples of the adult population, but on measurements from armed forces personnel in the USA: e.g. Garrett (1971), Greiner (1991), Donelson and Gordon (1996). Other data comes from industrial workers: e.g. Nag, Nag & Desai (2001), Saengchaiya & Bunterngchit (2004). In most cases, hand spans are not measured. From measurements of many different features of the human hand in the US (Garrett, 1971), depending on the characteristic measured, differences between males and females generally range between 10% and 20%. Some comparative hand anthropometry data, e.g. Saengchaiya & Bunterngchit (2004), Nag, Nag & Desai (2003) and Mandahawi et al (2008), clearly show that people of Asian descent have generally smaller hands than Caucasians.
Wagner (1988, p.117) noted that, based on studies prior to that time – particularly a study by Matzdorff (1968) – musicians tend to have greater hand and finger spans than non-musicians. Looking at a range of recent data on hand lengths and widths, there is no apparent difference between pianists and general adult populations in terms of hand length, though pianists’ hands tend to be narrower. (A detailed statistical analysis has not been done.)
A recent study of professional orchestral musicians in Australia (Driscoll & Ackermann, 2012) found mean thumb to fifth finger (1-5) spans to be similar to those found in the Australian study of pianists described here: Hand span data – recent Australian study . A separate survey of the hand spans of university business students is described in the paper by Boyle, Boyle & Booker (2015). Their hand spans (particularly 1-5 spans) were found to be noticeably smaller than those of the adult pianists. While gender and ethnic differences are again apparent, the average span for Asian males is markedly smaller than for the same group in the survey of pianists. This student survey also recorded heights; analysis of the data showed height to be a relatively weak predictor of hand span. See: Hand span versus height
The reasons for pianists having larger hand spans than the population at large is discussed in the paper by Boyle, Boyle & Booker (2015). While it is concluded that the effect of playing the instrument over a long period of time may be a factor, that effect is not likely to significant in terms of magnitude (0.2 inches for 1-5 spans at most). The effect of self-selection is most likely relevant, i.e. pianists who have bigger spans are more likely to achieve success and find piano playing enjoyable, are thus more likely to continue playing into adulthood.