Figure 9: Gamma function basics. Illustration of consequences of using several sequential pools in representing a clinical category. Results for a single pool (a), two pools ( 𝑏 2 ), three pools ( 𝑐 3 ), four pools ( 𝑑 4 ), and eight pools ( 8 ) are given, showing in each case the value of the state variable for the final pool in the sequence. For 𝑚 pools, the rate constant 𝑘 m has been set to give the same mean overall transit time of 𝑚 / 𝑘 m = 4 day (indicated by ■). For each curve, the maximum value (●) denotes the most probable overall transit time.