Greetings folks!

Working on a doctoral dissertation. I am trying to find empirical studies to substantiate the numbers frequently put forth by Wilber concerning the percentage of the population at each Stage/Tier. For example:

Wilber says in “Integral Psychology” (2000) beginning on p. 49: Beige 0.1% of adult population, Purple 10%, Red 20%, Blue 40%, Orange 30%, Green 10%, and then Second-tier 1%.

In “Integral Spirituality” (2006) 2nd-tier is said to be 2% (p. 196), Amber 40%, Orange 50%, Green 20%, and Turquoise 2% (p. 245).

Fast-forward some years to “Integral Meditation” (2016) and he states Amber 40%, Orange 50%, Green 25% (saying they don’t add up to 100% due to overlap) (p. 63), 2nd-tier is around 5% (p. 72), and 3rd-tier 1/10 of 1% (p. 75).

Can anyone point me to some studies that have been done to designate percentages at various Stages/Tiers?

Much gratitude…