You won't find any truly representative data on the prevalence of dynamic "overpronation at the STJ". No large-scale epidemiological studies have looked at this.
However, the Cheshire Foot Pain and Disability Survey (link
) reported the following prevalence of self-reported
...and the Feet First study of 784 people aged over 65 in the US (link
) reported an overall prevalence of flat feet of 19%. Their definition of a flat foot was one in which "the examiner was unable to insert his/her fingers under the arch of the foot with the respondent in a standing position".