1. A computer implemented method of determining whether a diagnostic model is accurately applicable to a population of subjects to which the model is applied, the model being configured to determine a biological state of a subject, the model being based on a set of data streams, each of the data streams being obtained by performing an analysis of biological samples taken from subjects of known biological states, the model having at least one diagnostic cluster located in a vector space having at least three dimensions, each dimension corresponding to a vector common to the data streams in the set of data streams, the diagnostic cluster having a centroid located at an initial centroid location based on locations of vectors from the set of data streams that correspond to the diagnostic cluster, comprising: receiving a vector set, the vector set including at least three vectors from a data stream obtained by performing the analysis of a biological sample taken from a subject of an unknown biological state; mapping the unknown vector set into the vector space using a suitably programmed computer; if the unknown vector set maps into the diagnostic cluster, calculating an updated location of the cluster centroid based on a combination of the location of the vectors from the unknown vector set and the set of data streams that correspond to the diagnostic cluster; determining the distance between the initial centroid location and the updated centroid location; and if the distance between the initial centroid location and the updated centroid location is greater than a predetermined threshold, providing an output indicating that the threshold has been exceeded which is indicative that the diagnostic model is not accurately applicable to the population of subjects to which the model is applied.