Force field behavior could change with combinations of functional groups, thus we repeated this calculation with pairs of Checkmol descriptors. We can apply Equation to analyze pairs of descriptors by replacing with + to represent molecules containing both descriptors. However, with pairs of descriptors, we are more concerned about if the combination of the descriptors is important. For example, if both descriptors and are highly probably in a set of molecules, then finding the combination in that set at a higher frequency is not particularly interesting. Thus, we try to determine if the descriptor pair is more likely to show up in a set of interest than the individual descriptors separately. To that end we calculate an enrichement factor given by