Misunderstandings can be eliminated, errors corrected, and conflicts resolved. There is no possibility of avoiding the use of models. There is only a choice of whether to use a mental model or a computer model. National development is a complex process, and no human mind no mental model can reliably trace out the future implications of all the relationships involved. We need the assistance of computers for issues as complex as development planning.
Computer models are just an expression of many people s mental models.
We can and should have confidence in the results provided we understand and agree with the assumptions and relationships. T 21 is based on highly respected mental models from dozens of fields and specialties, and they have all been expressed in a common, transparent, understandable framework. Clear diagrams and instant access to every assumption, equation, and data item in the whole model make the model uniquely transparent as a development-planning model. That said, T21 does not make predictions, and there are limits to the precision of the results. The model is a tool for comparing and evaluating alternative development-planning scenarios.