a true mean BFD (µpop) less than 42.7 mm will pass FAT. Furthermore, under these conditions a design that just passes FAT with µpop = 42.7 mm will cause 10 percent of the individual body armor plates to experience BFDs 44 mm. In fact, 5 percent of the plates will have BFDs 44.3 mm and 1 percent will have BFDs 45 mm.
This effect can be illustrated as follows. First consider a hypothetical armor system that has negligibly small variance in true performance. If the backing material exhibits a variance characterized by a standard deviation σbckmatl, then the true population of BFDs will be
where µpop is the mean BFD for that particular armor system (which depends on the mechanical response of the armor and the elastic recovery in the backing material) and σpop= σbckmtl. For µpop = 42.7 mm and with σpop = 1 mm, Figure G-1 shows the distribution of BFDs for the hypothetical population of body armor.
The impact of employing a measurement technique that adds significant variability is illustrated in Figure G-2. In this illustration, we assume the