A range of numbers is usually reported in numerals with an en-dash “–” (not a hyphen, “-“) between the numerals.
Early results have estimated the recidivism rate to be 16–40%.
Conkey, Margaret W. & Gero, Joan M. (1997). Programme to Practice: Gender and Feminism in Archaeology. Annual Review of Anthropology. 1997 (26), p. 411–437