Fig. 1.

Effect of clustering method on the number of OTUs. We created OTU clusters of the three known template preparations using combinations of multiple sequence and pairwise alignments, complete-linkage and average-linkage clustering, and single-linkage preclustering. Each method provides distinctly different numbers of OTUs for the same data. For short hypervariable tags sequenced at depth, the single-linkage preclustering using pairwise alignments, followed by an average linkage clustering (SLP / PW-AL) provides the most accurate results.