Contango Strategies (Canada)

UniFrac is a well-known tool for comparing microbial communities and assessing statistically significant differences between communities in meta-genomic studies. We identify a discrepancy in the UniFrac methodology that causes semantically equivalent inputs to produce different outputs in tests of statistical significance.The phylogenetic trees that are input into UniFrac may or may not contain abundance counts. An isomorphic transform can be defined that will convert trees between these two formats without altering the semantic meaning of the trees. UniFrac produces different outputs for these equivalent forms of the same input tree. This is illustrated using metagenomics data from a lake sediment study. Practitioners should be aware of this issue and use the tool with caution to ensure consistency and validity in their analyses.