AFAIK, the AMR utilization is either equivalent to a full rate TCH or a half rate TCH, depending on the codec used.
It is absolutely equivalent to FR and HR occupancy of the radio timeslots.
Maybe your question is about AMR penetration rate in your market ? and how does it impact the traffic mix ?
Well, you have to base your studies on QoS traffic measurements (actual erlangs, and actual split of AMR and non-AMR calls…).