Fig 4. Scheme to illustrate the definition of levels and the calculation of entropy that is based thereon.

A-B): For one fictional case the spatial heterogeneity and the in-case variance for one variable is illustrated (number of follicles per slide in Fig 2A and atrophy grading in Fig 2B). The numbers of follicles per slides were mapped to one of 10 levels (with an interval of 5 lymphoid follicles; accordingly level 0 = <5 follicles; level 1 = 5 - < 10; etc.). The resulting frequencies / relative probabilities are plotted next to the scheme. C-D): Entropy as calculated for the number of follicles in case 37T004 C) Fictional thymus with a non-random, completely homogenous distribution of measurements for the number of follicles. The corresponding entropy equals zero. D) Mean-values and standard deviations of the number of follicles per region in CD23-stained sections of case 37T004. The entropy value in this case with heterogeneously distributed follicle frequencies across the various regions is 2.2bit.