The complexity of different cell types in different organs frequently confounds biochemical estimates of cell number by the determination of the amount of DNA, or maceration of tissues. Assumptions made about particles and how they introduce Bias in the determination of particle number Shape of the particle Much of the theory and methodology relating to counting numbers of particles is related to geometrical probability. The assumption made in many stereological methods is that the particle is a sphere. Most formulae used in the calculation of particle number assume that the particle is regular and the approximations are special cases of the sphere eg . This is alright for spherical particles eg .
Mitochondria are frequently ellipsoid and can be branched, cell nuclei are frequently ellipsoid.
Sampling errors Sampling errors are a major cause of concern. The probability of recognising a particle and counting it, depends on several factors including section thickness, section angle, particle size and shape. This is important for several reasons relating to the dimension of the sample, usually a slice, taken through the specimen. The information is essentially 2D and provides information about 'profiles' of particles inside sectioned material. In the figure above our section clearly has cut large particles and not small ones.