[Eaglefixer]

Having done my masters thesis on a large computer simulation I can say that without full validation with actual past data the computer models mean less than nothing.

[LTCJ]

Having done my masters thesis on a large computer simulation I can say that without full validation with actual past data the computer models mean less than nothing.

Very good. A one line refutation of global warming.

We were taking about global warming, weren't we?

[Steve Schulin]

There's surely many serious issues related to the use of models by policymakers. My interest has grown in this subject over the past couple of years as it relates to the modeling of climate. I've become persuaded that such models can be very useful for understanding various interconnections, but they are inherently of dubious predictive value. "Validation" of the model as a whole doesn't rule out possible non-uniqueness of the results, so the changes in the particular variable you're interested in may be quite incorrectly handled. Is this a problem with macroeconomic models, too?

[Rifleman]

yah. Expecting to get meaningful qualitative results out of a model of a nonlinear system over more than the short term is a sign of someone who doesn't understand the math.