SLA packet loss base

Some people replied me about my questions. thanks for reply.
However, what I want to know ultimately is something like technical proof or standard or experimentation information
they can logically support SLA values in provider's IP network.
For example, regarding packet loss, I found information it is based on voip service tolerance (al least below 1% packet loss).
but some provider announce they can guarantee 0.3% packet loss. Where does 0.3% come from ?
Can anyone give me an answer about this question ? In fact I am going to make some guideline of network quality of my network.

Best regards,

Take a look at the BRIX active measurement instrumentation product which is now owned by EXFO. Many carriers use the BRIX probes to produce empirical data representing SLA values such as jitter, packet loss and round trip times for their network links. BRIX also has other more sophisticated application tests (VoIP codecs, etc.) which can be run from their distributed probes to any network end-point.