Clinical guidelines developed by NICE are published with the expectation that they will be regularly reviewed and updated as necessary. Any decision to update a guideline must balance the need to reflect changes in the evidence against the need for stability, because frequent changes to guideline recommendations would make implementation difficult. There are inherent risks that a new and less exhaustive surveillance methodology (for the 2-year, 6-year and 10-year reviews; see section 4) might have a lower sensitivity to determine which guidelines need updating, although these risks will be balanced against a new surveillance process that will allow decisions to be revisited more frequently.