The interpretation and cross-laboratory comparison of data obtained by the above-mentioned methods is complicated by the fact that permeation typically occurs across multiple lipid bilayers, whose exact count is rarely known or reported. Another common feature of the above methods is that the permeation area is limited to a few square cm, which means that very long measurement times are needed in the case of low-permeability substances. Therefore, significant efforts have been devoted also to the development of computational methods for determining membrane permeability and partitioning of individual molecules .