Evidential reasoning for WebTrust assurance services

We study two aspects of assurance services in electronic commerce. The firs t deals with the type(s) of evidential networks that will allow a professio nal accountant to provide assurance. Here, we develop an evidential network model for "WebTrust Assurance," a service being provided by the American I nstitute of Certified Public Accountants (AICPA) and the Canadian Institute of Chartered Accountants (CICA). Our model augments the AICPA/CICA approac h and provides goals, subgoals and evidence relevant to the overall assuran ce to be provided. The aggregation of evidence and the resolution of uncert ainties follow the belief-function approach. Next we develop a decision-theoretic model for the assurance-planning probl em. Our approach is based on estimating the expected value of providing var ious levels of assurance and is illustrated with several different scenario s that may be faced in practice. We also consider the role of ambiguity in decision situations such as planning WebTrust engagements and calculate bou nds in expected value based on whether auditors are conservative or not in their approach to risk.