A well-characterized reference dataset can be used to test hypotheses and, conversely, to derive testable hypotheses from the reference itself. For instance, inflammatory bowel disease has been observed to be associated with a microbial dysbiosis index (MD-index) that is the ratio of the relative abundances of a set of pro-inflammatory taxa to a set of anti-inflammatory taxa [32]; a robust reference set would allow assessment of the hypothesis that diet or lifestyle factors are strongly correlated to this index within the general public as well. In an opposite example, a significant correlation between diversity and time of the year was observed in the American Gut reference set [33]. Because it appears that individuals have a higher diversity during the holiday season in the US, one might hypothesize that it is the holidays and not the time of the year that drives the correlation—possibly due to changes in exercise and diet patterns. This putative effect can then be tested once the project acquires sufficient samples from western countries in the southern hemisphere.
