The effect of increasing human nucleic acid on the hybridization signal. Three quantities, 200, 10 and 0 ng of human lung RNA (panels a, b, c), were hybridized to a pathogen microarray comprised of ~38,000 probes. The fluorescent signal from the pathogen-specific probes was log-transformed and used to generate histograms. An expected normal (Gaussian) distribution is depicted by the line in the above figure. Tests for normality indicated significant deviation, with the following Kolmogorov-Smirnov Z values: (a) 41.5, (b) 14.6, (c) 12.1 (all p < 0.01).