he original, first-order Kakugo method is extended to find second-order reactivity ratios of homogeneous catalysts in ethene/propene copolymerizations based on triad fractions. Subsequently, the first- and second-order reactivity ratios of eight Si-bridged C2-symmetric ansa-zirconocenes or hafnocenes, as obtained by the Direct Peak method, are used to compare with the Kakugo methods. From the results it is clear that the second-order methods give better descriptions than the first-order methods. Only the results of the second-order Direct Peak method are statistically justified, reflecting reliabilities >99.5%. Though the Direct Peak method in all cases gives the most reliable reactivity ratios, the second-order Kakugo method turns out to be a practical tool to find estimates.