[davidvaughan]

Although the learning pyramid may be accurate, the research on which the figures is based has either gone missing or never existed.

The given source is the National Training Laboratories in Bethel, Maine. However, they happily admit that they're unsure how it came to have figures.

"Yes, we believe it to be accurate - but no, we no any longer have - nor can we find - the original research that supports the numbers. We get many inquiries every month about this - and many, many people have searched for the original research and have come up empty handed.”

http://www.virtuala.com.au/essays/learningpyramid.html