What does it mean if both unweighted and weighted unifrac is statistically significant between 2 samples?

[macrobiome (T)]

Does it mean that there is significant correlation in terms of the bacterial species present without factoring in their abundance as well as that when abundance is factored in (weighted), the abundance of respective species is also significantly correlated?

[SoilRotifer (Mike Robeson)]

Hi @macrobiome,

I'd highly recommend reading one of my all-time favorite articles:

Lozupone, Catherine, Micah Hamady, Scott T. Kelley, and Rob Knight. 2007. “Quantitative and Qualitative Beta Diversity Measures Lead to Different Insights into Factors That Structure Microbial Communities.” Applied and Environmental Microbiology 73 (5): 1576–85. http://dx.doi.org/10.1128/AEM.01996-06

This article provides insight on how to interpret the qualitative / richness leaning metrics (e.g. Unweighted UniFrac, Jaccard), vs quantitative / evenness leaning metrics (e.g. Weighted Unifrac, Bray-Curtis).

For example, here is some text taken from the article:

"... unweighted UniFrac clustered the samples mainly by temperature, suggesting that the main effect was whether lineages could survive in each of the different springs."

"... weighted UniFrac will be suitable for studying transient changes in microbial communities related to nutrient availability and may also be suited to the analysis of seasonal changes and changes under the influence of different pollutants..."

Note: these interpretations may not apply across all study systems. But they do provide a framework by which you can compare and contrast how these measures can be interpreted.