CAD Productivity

I hope this request does not duplicate any recent discussion on this list.
 I just joined today, because I had to find some new sources for a
difficult request which of course is needed asap.  The question:  Has
anyone done any benchmarking or other productivity type study of CAD in
architectural firms?  That is - can it be proven that using CAD is more
efficient than not using it?  Any information would be appreciated.
Anelle Kloski, Facilities Design & Construction Lib., Oakland CA.
(akloski@xxxxxxxxxx)