Well, there are many potential issues.
One reason is that they don't all look at all the same data.
For example, looking at this nomogram.org calculator of local recurrance after surgerynomogram.org/Prostate/pros_calc.php
It assumes that a Gleason 4+3 is the same as a Gleason 3+4 which other evidence shows is not really the case. So it will be over-optimistic for one and overly pessimistic for the other.
Second, in comparing nomograms be careful that the end-state of the two is the same. If one of them predicts cancer specific mortality and the other predicts biochemical recurrence, the answers they generate will be *very* different. Make sure the time periods are the same.
Third, the SMK nomos assume patients are treated at a first rate major cancer center by an experienced surgeon, and some of the others may be based on what happens for average people in a community seeing doctors with a wide range of experience and skill
4th, the studies may have different degrees of ability to follow up over the long term, so data can get lost.
5th, the studies may have different entry criteria which may lead some of them to have patients with more aggressive cancers, or older patients with greater likelihood of dying of something else first.
In any case, after allowing for these kids of differences the nomogram.org calculator for post surgery outcome and the SMK calculator for the same gave me similar results in my particular case. So the agreement or lack thereoff may not be evenly distributed.
Post Edited (proscapt) : 4/23/2011 4:04:03 PM (GMT-6)