There has been some movement of some of the typical book based media
towards  e-books (primarily pdf format) and towards audio books. In
some instances these are instead of print/book and in other instances
it may be in addition to or as an option of one or the other. One
hears that this is going to be significant - and others I hear say
that e-books were less popular than they were for a while.

My questions:
1 - Are there any statistics from reliable studies that quantify the
impact it has had on the volume or dollars of print media.
2- Is this trend truly continuing and is it expected to continue--as
evidenced by expert opinions or by investment in machinery investment
to prepare for this perceived trend or any other evidence?