Differential, defined minimum, meaning

In either approach, if the goal is to compare close titer values (such as eightfold difference between titers of two ADA samples), it is important to apply the interpolation method to determine the titers, or if a noninterpolation method is used, the serial dilutions should be narrowly spaced (ideally twofold or less). In addition, an objective method is needed for determining the ability of the assay to differentiate titers (titer precision). This titer precision is defined by the minimum significant ratio (MSR), which is the smallest fold change between the titers of any two ADA-positive samples that can be considered as significant. For example, MSR = 5 means that at least a fivefold difference in the titer results between any two positive samples will be required to conclude that they are statistically different. Evaluation of MSR is mostly relevant when comparison of samples with close titers is of interest. 

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