What are you aiming to achieve? There is a capability of the Virtuoso Variation Option used with ADE Explorer/Assembler for doing high-yield verification using an approach called Scaled Sigma Sampling which allows you to verify the yield with high sigma targets like six sigma. This approach (giving an over-simplified description) runs a monte carlo simulation with various scale factors of the sigma, and then from the results can then compute the yield. Because it scales up the sigma, it has the benefit of actually simulating points in the failure regions - trying to simulate 6-sigma or beyond in normal monte carlo is very unlikely to simulate anything in the tails because the probability of them happening is very small.

By the way, there is no tool called "cadence", so it helps if you can be precise about which tool/product you're using. Cadence is the name of the company providing EDA tools, not the name of a software suite (and Cadence produces a very wide range of EDA software, so you could be talking about many things).

Andrew.