A computer-implemented method for determining the likelihood of Gl tract dysbiosis in a subject, said method comprising: (i) 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 Gl tract of the subject and wherein each level of each microorganism or group of microorganisms is a profile element of said test data set, (ii) applying to said test data set at least one loading vector, wherein said at least one loading vector is at least one orthogonal latent variable determined by the regression analysis of the levels of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects, thereby producing a first projected data set, (iii) providing said first projected data set, (iv) from said first projected data set calculating the Q-residual of the microbiota profile and comparing the Q-residual of the microbiota profile with a normobiotic to dysbiotic threshold Q-residual value determined from the corresponding analysis of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects and/or subjects with dysbiosis, (v) from said first projected data set calculating the Hotelling's T 2 for the microbiota profile from the variance explained by the orthogonal latent variables determined by the regression analysis of the levels of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects of step (ii) and comparing said Hotelling's T 2 for the microbiota profile with a normobiotic to dysbiotic threshold Hotelling's T 2 value determined from the corresponding analysis of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects and/or a plurality of subjects with dysbiosis, wherein step (v) may be performed before or after or concurrently with step (iv), and wherein a microbiota profile with a Q-residual or Hotelling's T 2 in excess of said respective thresholds is indicative of a likelihood of dysbiosis. (i) 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 Gl tract of the subject and wherein each level of each microorganism or group of microorganisms is a profile element of said test data set, (ii) applying to said test data set at least one loading vector, wherein said at least one loading vector is at least one orthogonal latent variable determined by the regression analysis of the levels of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects, thereby producing a first projected data set, (iii) providing said first projected data set, (iv) from said first projected data set calculating the Q-residual of the microbiota profile and comparing the Q-residual of the microbiota profile with a normobiotic to dysbiotic threshold Q-residual value determined from the corresponding analysis of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects and/or subjects with dysbiosis, (v) from said first projected data set calculating the Hotelling's T 2 for the microbiota profile from the variance explained by the orthogonal latent variables determined by the regression analysis of the levels of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects of step (ii) and comparing said Hotelling's T 2 for the microbiota profile with a normobiotic to dysbiotic threshold Hotelling's T 2 value determined from the corresponding analysis of said plurality of microorganisms or groups of microorganisms in corresponding Gl tract samples from a plurality of normal subjects and/or a plurality of subjects with dysbiosis,