From Muslim Statistics:
38.14% (Mean) average would translate to 793,312,000 Muslims. The Muslim population worldwide in 2014 was estimated to be 2.08 billion people. The demand for women to wear a full covered cloak is not a religious obligation within Islam, but is a demand originating by extremist groups.
Full body and face coverage with a Burka or Niqab is a dress created to warn women that if they do not hide, they face rape and abuse. The reasoning being that they invite and deserve these crimes by their own volition, unless they cover up.
The full report explains:
The style #1 is en vogue in Afghanistan; #2 is popular among both conservatives and fundamentalists in Saudi Arabia and other Persian Gulf Arab countries; #3 is the style vigorously promoted by Shi’i fundamentalism and conservatives in Iran, Iraq, and Lebanon; #4 and #5 are considered most appropriate by modern Muslim women in Iran and Turkey; and #6 is preferred by secular women in the region.
Unsurprisingly, Saudi Arabia ranks highest for the most conservative clothing preference, as 63% of respondents pointed to the face-concealing niqab style as the most appropriate covering. On the other side of the spectrum, 32% of Turkish respondents and 49% of Lebanese respondents said that they considered an uncovered head to be most appropriate.
Overall, most people surveyed considered the conservative hijab look of woman #4 to be the most appropriate dress for public. The study also investigated responses to the question, “Should women be able to choose their own clothing?”