Principal component analysis for bacterial phylotypes and gastrointestinal symptoms. Principal component analysis (PCA) for eight bacterial 16S rRNA gene phylotypes and four gastrointestinal symptoms in the (a) before the probiotic intervention (0 months) and (b) during the intervention (combined second and third time-points, 3 and 6 months). Placebo and probiotic groups are denoted in blue and red, respectively. The arrows in the biplot represent the association of the original variables with the samples in the PCA visualization: their length and location are proportional to the variable loadings on the two first principal components. In Figure 1a, the first and second principal components (PC1 and PC2) explain 20.3% and 15.3% of the observed variation, respectively. In Figure 1b, the first and second principal components explain 24.6% and 15.4% of the observed variation, respectively.