Fig. 4

Oral Wash Alpha Diversity Is Associated with Sputum Alpha Diversity. Circles represent FE samples while triangles represent IE samples. Linear models were used to predict sputum alpha diversity based on oral wash alpha diversity. The solid lines represent the aggregated model incorporating both phenotypes while the dotted lines represent the models of frequent or infrequent exacerbator samples alone. a) Oral wash Shannon diversity alone was a significant predictor of sputum Shannon diversity (p = 0.0002), but addition of phenotype and the interaction of oral wash Shannon diversity and phenotype to the model resulted in a near-significant oral wash result (p = 0.07) and non-significant results for phenotype and their interactions. b) Oral wash Simpson diversity alone was also a significant predictor of sputum Simpson diversity (p = 0.0003), and incorporation of phenotype and its interaction resulted in significant results for oral wash diversity (p = 0.008), but non-significant results for phenotype and its interaction with oral wash diversity. The removal of the low diversity x-outlier (boxed in both panels, see text and Additional file 1: Figure S2) resulted in non-significant results for all but oral wash Shannon diversity alone as a predictor of sputum Shannon diversity (p = 0.039)