First, congratulations for wanting to have faith in your staff. Good bosses believe their staff is capable of doing their jobs and should make every effort to let them know. But before you go shredding the personnel reviews and possibly ending up in hot water, check to see who wrote them. If it was one person, as opposed to several, consider that he or she may have had an axe to grind or was just being petty out of insecurity. Any time managers have only negative things to say about employees, it's a safe bet that they're the ones with the problem, not the employees. So be careful not to give reviewers instant credibility.
We suggest that you start fresh with your staff. Pretend these reviews don't exist and give your employees full support. You may find that as a supportive boss, they'll feel re-energized and perform at their highest level. It's far more important to honor those who work for you than to let suspect documents guide your course. In time you'll learn what's accurate, and we're betting that by choosing to put your faith in the people you work with, everyone will end up winning.