This Recommendation introduces some of the more common types of mean opinion score (MOS) and describes the minimum information that should accompany MOS values to enable them to be correctly interpreted.
ITU-T P.800.2-2013 history
2016ITU-T P.800.2-2016 Mean opinion score interpretation and reporting (Study Group 12)
2013ITU-T P.800.2-2013 Mean opinion score interpretation and reporting (Study Group 12)