In literature, several methods of estimating confidence intervals for reactivity ratios have been published during the last decades . These methods are based on different mathematical approaches and strongly differ in applicability, complexity of the calculation procedure as well as availability. A classification of all approaches may be done by comparing their validity for different error structures and models. Firstly, the error structure of f 2 and F 2 is crucial. Here, it is necessary to distinguish between three different error structures: (i) an error on the dependent variable (F 2 ± ∆F 2 ), (ii) errors on both variables (