a different value for each species, chip and PIC respectively; and are multipliers of the homopolymer length and flow cycle respectively; and is a constant. is similarly defined, with different values of the coefficients and the exponentiation to ensure a positive variance. Unlike Roche 454 pyrosequencing, where the prevalence of errors are a consequence of increasing variance in flow-calls (with insertions and deletions approximately equally likely [14]), it would seem that both the mean and variance are contributing to the over-call/under-call rate in Ion Torrent PGM sequences.
