For VOIP Test, How to Verify the Accuracy of the Quality Report Including Packet Loss, Jitter, Latency Etc.?

I have a VOIP report when impairment is injected. This report contains MOS score, R-Factor (Listen, and conversation) etc. But how do I verify these figures are correct or accurate? If I need to use a 3rd party tester, what is that? I have tried to follow G.1050 standard, anyone ever used this one or any better suggestion, thanks.