We have built on the recent work of Campbell et al. , which suggests an optimal analytical model for the study of Langmuir-Blodgett monolayers with neutron reflectometry. The Bayesian model comparison method is used to investigate the relative evidence for three models described by Campbell et al., with particular focus given to the number and type of isotopic contrasts present in the experimental datasets. This method has shown that when seven isotopic contrasts were under consideration, there was clear evidence for model 3, in agreement with the work of Campbell et al.. Additionally, it was observed for the most commonly measured combination of isotopic contrasts, when d 70 -ACMW, d 70 -D 2 O, and h-D 2 O were considered, there is still clear evidence for model 3.