What's the overlap between Sufi Muslims and Sunni and Shiite Muslims?

Question

A Pew Poll has given the percentages of Sunnis, Shiites, and those who identify as "just a Muslim" throughout the world. Each of these is considered mutually exclusive by the pollster. Then it says:

For some Muslims, another layer of identity comes from membership in a Sufi order. ... These orders can fall within either Sunni or Shia Islam.

It then gives the percentages of Sufis in various countries, as it had for Sunnis and Shiites. But it doesn't really give an idea of the overlap between them.

Have any polls or studies said how many Sufi Muslims also adhere to Sunnism or Shiism?

Answer 1

You write: “From these numbers I could derive vague approximations for how many Sufis are also Sunnis and/or Shiites”. I do not understand how (purely statistically) you could do this. Perhaps you could explain.

Most Sufis consider themselves to be followers of one or another of the law schools (madhāhib), either Sunni or Shi’i. In Egypt and North Africa (for example) the majority of the population as a whole, and thus also of the Sufis, follow the Maliki school of Sunni Islam. In Iran the Sufis, like the majority of the population as a whole, follow the Ja’fari school of Shi’i Islam. In the Yemen (if I may speak from my personal experience) the Zaydi (Shi’i) ulama reject Sufism entirely, but the Shafi’i (Sunni) believers are often Sufis.