add ANOVA analysis assay and protocol

assays/ANOVAForDifferentialEnrichmentOfMetabolites/protocols/ANOVAForDifferentialEnrichmentOfMetabolitesProtocol.md

+## ANOVA for differential enrichment of metabolites
+
+We applied the python package *statsmodels* (Seabold, S. and Perktold, J., 2010) to perform two-way analysis of variance (ANOVA) (Girden, E., 1992). For a particular metabolite, we collected its mass spectrometry relative response in the WT or in sweet knockouts (line: WT vs. SWEET), and at different segments of the root (region: 2cm vs. 4cm vs. 6cm vs. whole). We fit a model that decomposes the relative response of the metabolite as a combination of line-specific and region-specific factors; this model is described by the following string in the code: *‘relativeResponse ∼ Line + Region'* and calculates a *P*-value for *Line* and one for *Region*. Using the *P*-value cutoff of 0.05 for *Line* (and *Region*), we determined the relative response of the metabolite to change significantly with *Line* (*Region*) if *P* <0.05.
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