The invention provides a method for determining the likelihood of GI tract dysbiosis in a subject, said method comprising providing a test data set, wherein said test data set comprises at least one microbiota profile, said microbiota profile being a profile of the relative levels of a plurality of microorganisms or groups of microorganisms in a sample from the GI tract of the subject and wherein each level of each microorganism or group of microorganisms is a profile element of said test data set, applying to said test data set at least one loading vector determined from latent variables within the profiles of the levels of said plurality of microorganisms or groups of microorganisms in corresponding GI tract samples from a plurality of normal subjects, thereby producing a first projected data set, applying to said first projected data set a transposed version of said at least one loading vector, thereby producing a second projected data set, comparing said test data set with said second projected data set and combining the differences between the corresponding profile elements of the second projected data set and the test data set and comparing the combined differences with a normobiotic to dysbiotic threshold value determined from the corresponding analysis of said plurality of microorganisms or groups of microorganisms in corresponding GI tract samples from a plurality of normal subjects and/or subjects with dysbiosis, applying at least one eigenvalue to said first projected data set, said eigenvalue determined from said at least one loading vector, and combining the resulting values for each profile element and comparing the combined values with a normobiotic to dysbiotic threshold value determined from the corresponding analysis of said plurality of microorganisms or groups of microorganisms in corresponding GI tract samples from a plurality of normal subjects and/or subjects with dysbiosis, wherein a microbiota profile with said combined differences or said c
