As Ericsson explains CCALLS can be stepped several times during a call setup, due to for instance congestion or several received Random Accesses (RAs) from a mobile. This could result in very high values for these counters in problem cells and should be considered with care in those cases. The formula below has compensated for the attempts at congestion.
The number of SDCCH establishments in relation to the number of seizure attempts (when no SDCCH congestion) can be calculated as follows
S_est=CMESTAB/(Ccalls-(Ccongs+Ccongssub))
Hope this will clarify the issue.