Effects of type of nucleotide mismatch on the ratios of signal intensity of PM to those of cognate MM probes in the target concentration of 1.4 pM. The signal intensities of PM probes were averaged over probes of all lengths. Those of MM probes with mismatches in all positions were grouped by type of nucleotide mismatch and averaged for the group. The signal intensity ratios are expressed as geometrical averages for each type of nucleotide mismatch. Values in parentheses represent standard deviations. To distinguish types of nucleotide mismatch, the types of nucleotide of the target and probe are indicated in rows and columns, respectively.