Figure shows the reflectometry and scattering length density profiles that will maximise the likelihood of each of the models, when a dataset containing all seven isotopic contrasts is evaluated. From the investigation of the agreement between the measured and modelled reflectometry, it may be observed that model 3 gives the best agreement to the data. Furthermore, on the investigation of Figure , the evidence for model 3 is substantially more than for models 2 or 1, as determined from Equation . This result agrees well with the outcome of the Campbell et al. , where model 3 was found to offer the minimum χ 2 value. Additionally, it agrees with the use of a two-layer, roughness-containing model, such as that which was used previously to analyse this data However, the above example, where the dataset contains all seven isotopic contrasts is extremely idealised. It is very rare for a neutron reflectometry dataset to contain this number of isotopic contrasts; in part due to the high cost and difficulty in preparation of deuterated chemicals. For example, in the work of Campbell et al. the contrasts that were investigated were tail-deuterated phospholipid on D 2 O and ACMW and fully-hydrogenated phospholipid on D 2 O and ACMW. Furthermore, the recent works of both Pabios et al. and Ortiz-Collazos et al. investigate tail-deuterated phospholipid on D 2 O and ACMW and fully-hydrogenated phospholipid on only D 2 O and these particular contrasts are commonly utilised in the literature when a two layer model is ap-plied .