Estimating O&P
Don,
There is a wealth of literature showing the O&P estimates are tainted in most cases. These "cardinal" values are most often uncalibrated.
One way out of this in our experience in aerospace and enterprise IT is to us an "ordinal" value scale (ABCDEF) and assign ranges to those values.
These too are uncalibrated and need to be fixed before much confidence can be applied.
The primary source of this approach is _Effective Risk Management: Some Keys to Success_, 2nd Edition, Edmund Conrow, AIAA Press, 2003. Ed's Appendix H describes "Some Characteristics and Limitations of Ordinal Scales in Risk Analysis."
While neither affordable or accessible (tough reading) Ed's book is mandatory for anyone working the programmatic or technical risk area.
