A method of estimating a concentration of DNA molecules in a biological sample includes storing a number of a plurality of reaction sites in a memory and distributing the biological sample among the plurality of reaction sites. The method also includes determining a number of the plurality of reaction sites characterized by a presence of one or more of the DNA molecules and computing a portion of the plurality of reaction sites characterized by the presence of the one or more of the DNA molecules. The method further includes estimating the concentration of the DNA molecules as a function of the portion of the plurality of reaction sites and computing a confidence interval for the estimated concentration of DNA molecules.