A method and apparatus are disclosed for modeling a system to estimate
values and associated uncertainties for a first set of variables
describing the system. A second set of system variables is selected,
where the second set is directly or indirectly causally related to the
first set of variables. Data is obtained or estimated for each variable
in the second set and the quality of selected data is appraised. A
network is formed with nodes including both sets of variables and the
quality appraisals, having directional links connecting interdependent
nodes, the directional links honoring known causality relationships. A
Bayesian Network algorithm is used with the data and quality information
to solve the network for the first set of variables and their associated
uncertainties.