http://www.usp.org/frequently-asked-questions/dissolution-performance-verification-testing-pvt
Factors affecting the PQ results:
Temperature not too significant linear
Speed significant 10-30%
Vibration significant 20-50%
Centricity reasonable ± 5-15%
Dissolved Gas significant ± 50%
Media pH reasonable ± 5-10%
Media Contamination significant ± 20-45%
Sampling Position not too significant 1-3%