A method for determining an unknown starting quantity of a target nucleic acid
sequence in a test sample comprises amplifying the unknown starting quantity of
the target nucleic acid sequence in the test sample and known starting quantities
of a calibration nucleic acid sequence in respective calibration samples; and determining
a respective threshold value for each of the nucleic acid sequences using a derivative
of a growth curve derived for the sequence. The starting quantity of the target
nucleic acid sequence in the test sample is determined using the threshold value
determined for the target sequence and a calibration curve derived from the threshold
values determined for the known starting quantities of the calibration nucleic
acid sequences.
