High Quality Content by WIKIPEDIA articles! In mathematics the signal-to-noise statistic distance between two vectors a and b with mean values a and b and standard deviation a and b respectively is: D_{sn} = {(mu _a - mu _b) over (sigma _a + sigma _b)}. This distance is frequently used to identify vectors that have significant difference. One usage is in bioinformatics to locate genes that are differential expressed on microarray experiments.