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¡@¡@This study aims to investigate the theories and empirical performance of the futures and options margin systems currently used in the domestic and international exchange houses. The current system used in Taiwan Futures Exchange (TAIFEX) is strategy-based rather than portfolio-based or and contract risk-based. It is no longer compliant with the development of the futures market. Therefore, it is suggested that TAIFEX should employ international experiences to adopt a portfolio-based and VaR-based margin system so as to meet the need of the local trading feature that portfolios contain both stock futures and stock options. ¡@¡@This study integrates scenario simulation and the diagonal model to propose a new model, called Beta-Simulation, to calculate the margins for portfolios containing stock options, index futures, and stocks. The proposed model can not only simplify the inter-commodity spread in SPAN but also theoretically improve the drawback of TIMS of using a simple credit offset multiplier. In the empirical test, back testing is performed on the margins calculated by Beta-Simulation with historic data of portfolios with stock options, and other common margin systems are also included in the test for comparison. ¡@¡@The empirical results reveal that only SPAN and Beta-Simulation can save approximately 12%~42% margin requirements for portfolios containing stock options, but under the same protection degree, Beta-Simulation requires significantly lower margins and a simpler calculation process than SPAN. Therefore, the proposed model is a better model of calculating margins and VaR for portfolios containing stock options.

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