A question often asked is how many people in the population can see in 3D. The answer varies from study to study, but one of the larger studies suggests that about 3% of people cannot see binocularly at all, a further 7% of people have some limited 3D vision and therefore about 90% of people have good 3D vision. However there are many factors that affect this and there is not one single reason for these variations.
In addition in the study reported in [Jones2001] even those people who fell into the 90% with good vision had a wide variation in their stereo ability.
This area is one of active research, and is where practical guidelines need to be established so that content and application producers can reliably create high quality images.