In this work, we have outlined and applied a rigorous and easy to implement framework for the Bayesian model comparison of analytical models used in neutron FIG. . Evidence for each of the models (x) in the presence of common combinations of isotopic contrasts; h-D2O, d70-D2O, d70-ACMW, d83-D2O & d83-ACMW (blue), h-D2O, d70-D2O & d70-ACMW (orange), and h-D2O (green). The associated reflectometry and scattering length density profiles may be found in Figures . The data and code used to generate this figure, and the figure file, are available under the MIT license as part the electronic supplementary information . and X-ray reflectometry analysis. Our particular implementation is freely available as Python code in the electronic supplementary information of this work . Similar methods were previously applied to model comparison problems in neutron reflectometry by Sivia and others . However, it is not commonly applied to modern reflectometry analysis; despite the clear benefits.