Here's a report and analysis of another study of marathon vs. half marathon performances. This one is based on the results of approximately 600 finishers over two years who ran the same two HM and marathon races spaced 4 weeks apart. The researcher compiles the results into seven categories of marathon finishing times from sub-3 hours to 4:30+. He also analyzes the quality of marathon race pacing within each of the seven categories.
http://mysite.verizon.net/jim2wr/id209.html
I hope you fund it useful
Hanan