1. A method for quantifying nucleic acid sequences present in one or more amplification reactions to be collectively analyzed, the method comprising the steps of: acquiring intensity data for each reaction over a selected number of reaction intervals wherein the intensity data is indicative of a detected quantity of progeny sequences arising from each sequence; assessing the intensity data over the selected number of reaction intervals to generate an amplification profile indicative of the change in quantity of the progeny sequences for each reaction interval; evaluating each amplification profile to identify a corresponding exponential region, having upper and lower bounds; determining a threshold based upon an intersection between at least one exponential region upper bound with at least one exponential region lower bound; performing a polynomial fitting operation for each amplification profile that applies the threshold to determine a polynomial root which is thereafter associated with a threshold cycle for each reaction; and quantifying the sequence for each reaction using the threshold cycle.