set statistics simulate on tells the optimizer to optimize queries using simulated statistics:
set statistics simulate on
In most cases, you also want to use set showplan on or dbcc traceon(302).
If you have loaded simulated statistics into a production database, use set noexec on when you run queries using simulated statistics so that the query does not execute based on statistics that do not match the actual tables and indexes. This lets you examine the output of showplan and dbcc traceon(302) without affecting the performance of the production system.