Specificity and sensitivity of select cut-offs for individual microarrays. Specific (spiked B. subtilis and housekeepers) and non-specific hybridization control groups (plant, bacterial and viral genes) represent sensitivity (squares) and specificity (circles), respectively. The intersection point of the two graphs indicates the threshold TM at which Sp equals Se. TM values were 0.18 (array1) and 0.09 (array 2). Indicated thresholds a-d are described in table 1. The Tj values presented in Table 1 were used to construct these curves. Note the different signal range (abcissa values) for array 1 (A) and array 2 (B).