Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Drug specific parameters and parameter estimation
Tissue/plasma concentration ratios (Kp) were predicted for each tissue using the equations proposed by Poulin and Theil [24], Kp for the rest of body was optimised so that the predicted volume of distribution at steady state (VSS) is the same as the observed in vivo value using the following equation [25]
Kp;REST ¼ VSS;Obs VP
P Kp;T VT
70 P VT ð2Þ
The same Kp was assumed for adults and children and values for different tissues are presented in Table 1.
Category: