There is a whole lot of information out there on the failures, success, and attributes of projects and project management methods. Some claim the sky is falling and IT projects have an abysmal success rate. Others claim the have discovered the fountain of youth (their new methodology).
I came across a nice paper this morning "A Bayesian Truth Serum for Subjective Data," from MIT's Center for Innovation in Product Development. It describes some the problem of making subjective judgments - "Let's switch to this new software development methodology, since it will improve of quality and shorten time to market."
It's worth a read only to establish how to think about claims of fact in general.