Figure 4

OTU construction accuracy for the V5 'Artificial Community' as a function of percent sequence difference for the different noise removal algorithms. Results are given for the improved two stage 'AmpliconNoise' (A), the original 'PyroNoise' (B), single-linkage preclustering at 2% (C), and the DeNoiser algorithm (D). Reads classified as chimeric by comparison with the references were removed. The solid black portion gives the number of OTUs comprised of reference sequences and denoised pyrosequenced reads. These are good OTUs. The grey area OTUs formed only from reference sequences. These correspond to true OTUs that are missed. The diagonal shaded area those OTUs containing only pyrosequenced reads and hence are noise.