Figure 5.

The graph illustrates the kinetic relation between C_q value and PCR efficiency for efficiency values between 1.9 (solid blue line) and 1.7 (solid orange line) with an input of 10 copies of target in the reaction (yellow dot). The difference in efficiency values results in a range of C_q values between 35 and 42 cycles (vertical, solid light green lines). Because of the Poisson sampling variation, an average input of 10 copies per reaction will actually range between 5 and 18 copies. With the same PCR efficiencies (dotted blue and orange lines) the range of C_q values is extended with another 2.5 cycles (dotted green lines). The quantification threshold (N_q) is set at the level where the 10 copies of the input, with a PCR efficiency of 1.9, result in a C_q value of 35 (yellow arrow) [15]. The graph is based on the kinetic equation of PCR (Equation (1)).