Figure 4. The first principal component for the combined vaginal data, representing about 56 percent of the variance. The reference tree is colored by principal component sign (positive colored orange, negative colored green) and thickened proportional to magnitude. The edges across which maximal between-sample hetero- geneity is found are those leading to the Lactobacillus clade and those leading to the Sneathia and Prevotella clade. This axis corresponds to taxa that are important in the diagnosis of bacterial vaginosis, as Sneathia and Prevotella are associated with bacterial vaginosis, while Lactobacillus is associated with a healthy microbiome. [Matsen & Evans 2013]