where F i and f i are the mole fractions of the i-th component in the bulk and the (co-)polymer respectively. The quantities r i are the reactivity ratios of each propagating chain end. They are defined as the ratio r 1 ≡ k 11 /k 12 and r 2 ≡ k 22 /k 21 . Here, k i j are the propagation rate constants of the respective radical and monomer combination. Since equation ( ) is a non-linear equation (in the parameters r 1 and r 2 ), parameter estimation techniques via linear regression are prone to fail, yielding biased results. Furthermore, the data used to estimate the reactivity rations, pairs ( f 2 , F 2 ( f 2 )), have errors both in the dependent, F 2 , and independent f 2 variable. In addition, the errors may be correlated depending on the setup of the polymerization experiment. Using the correct statistical technique is therefore of paramount importance to obtain unbiased estimates of reactivity ratios. Including errors in the independent variable and incorporating the non-linearity of the problem can be done elegantly with the error-in-variables-method (EVM) . In 2018, Scott et al. used this method to provide an accessible EVM framework by providing a ready-to-use computational package.