AMR may lead to more drops

If the AMR traffic is increased,drop rate may increase as well in some situations.
I've read some technical research paper,which says that the robust of FR/EFR/HR is the almost the same as the SACCH frame,however,the robust of the AMR is better than the SACCH frame.That means that subscribers may disconnect the call by themselves when they encounter bad radio quality ,instead of more drop calls statistically ,when use of FR/EFR/HR.
However, in the same situations,subscribers may not disconnect the call since the quality still acceptable when use of AMR, at the same time,SACCH frame may not be able to decode,so it will lead to more drop calls statistically .

Also ,technical research shows that in some situations,handovers due to bad quality will increase .