The probiotics evidence-base represents a developing area of research endeavour, characterised by a myriad of approaches to research design from single-case to randomised controlled trials. The longitudinal nature of this design type and the current level of maturity of probiotics research activity, likely raises limitations for this type of design also, though potentially it is promising as the mechanistic underpinnings of action of probiotics becomes more understood. The 'gold standard' approach that may, at a stroke, enhance the credibility, standing and reach of probiotics research is the utilisation of the randomised controlled trial design. Irrespective of the type of design chosen for quantitative studies examining the influence, role, efficacy or mode of action of probiotics, it is noticeable in the literature that there exists large variability in the sample size of studies. Structural Equation Modelling offers a robust statistical 'glue' to bind together anticipated relationships between diverse variables and assess them statistically, robustly and pragmatically.