An error-in-variables-model (EVM) framework is presented for the optimal estimation of reactivity ratios in copolymerization systems. This framework consists of several sequential steps and practical prescriptions that can yield reliable and statistically correct reactivity ratio values. These steps include: (a) screening experiments for estimating preliminary reactivity ratios, (b) optimal design of experiments, (c) full conversion range experiments and estimation of optimal reactivity ratios, and if necessary, (d) design of sequentially optimal experiments and re-estimation of reactivity ratios and diagnostic checks. This complete methodology should become common practice for determining reactivity ratios with the highest possible level of confidence. The performance of this framework is verified experimentally with data from the controlled nitroxide-mediated copolymerization of 9-(4-vinylbenzyl)-9H-carbazole (VBK) and methyl methacrylate (MMA), a novel and largely unstudied copolymer system.