More than 12% of UK People Cannot See 3D…
[M]ore than one in ten of us (12%) has a visual impairment that means our brains are unable to correctly process the individual images that are transmitted to it via our left and right eyes.
This leads to an inconsistency in viewing the three spatial dimensions (height, width and depth) required to enjoy 3-D films in all their glory.
This is a UK survey, but I assume the results are similar for other countries.