u s application ser no ______ atty docket no ext 021 which is incorporated herein by reference the determination of a minimum number n of dna molecules that must be present in a sample to permit amplification and analysis of a low frequency target dna molecule is based upon a model of stochastic processes in pcr utilizing pre set or predetermined values for pcr efficiency and mutant dna to wild type dna ratio in the sample the model predicts the number of molecules that must be presented to the pcr in order to ensure within a defined level of statistical confidence that a low frequency molecule will be amplified the skilled practitioner will appreciate that determination of the minimum number n of molecules present in the sample may be used in lieu of or in addition to the enrichment techniques detailed above to ensure reliable results in the methods of the present invention alternatively methods of the invention may also be used to isolate total dna from stool homogenate the homogenized mixture is centrifuged to form a pellet made up of cell debris and stool matter and a supernatant containing nucleic acid and associated proteins lipids etc the supernatant is treated with a detergent such as 20 sds and enzymes capable of degrading protein e g proteinase k the supernatant is then phenol chloroform extracted the resulting purified nucleic acids are then precipitated by means known in the art a variety of techniques in the art can then be employed to manipulate the resulting nucleic acids including further purification or isolation of specific nucleic acids methods of the invention are also useful for analysis of pooled dna samples as described in more detail in u s application ser no 09 098 180 and.