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Steve Simon wrote : > There is an inherent distrust of SIMULATION models. Look at all the > controversy about simulation models for global warming. Quelle surprise ! Why shouldn't there be distrust of simulation modelling ? Almost all the simulation models I have seen are published with no external validation whatsoever. Often the data on which they are based is limited, and questionable assumptions are made. Global warming models are an excellent example, but one in which I will admit many modellers have done remarkably well :-).. Most of the models described over the last few years have been pretty poor. Yes the researchers have been working with both hands tied behind their backs because there is no way to externally validate the model - no alternative earths handy; historical data has been limited; and they have not envisaged the complexities of the system fully. Unlike many simulation models the results (of the last factor) have been that global warming models have almost universally under-predicted the rate of change ! The modellers have done "remarkably well" in that they have given us an inkling of likely problems, something many of us have found worthy of attention. So, of course we should examine simulation models critically, especially in light of the methodology applied, before they are published. They have their uses, but their limitations cannot be ignored. Mike. -- The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336.