One of the more recent developments in stereology is the proportionator. This method is likely to be one of the most sought after methods, not because it is new or flashy, but because it makes stereological work easier.

The most common stereological work in the biological sciences is counting cells.  In studies from toxicology to the neurosciences the basic question question is how many cells or structures are there. The first unbiased stereological technique was the physical disector. The next was the optical fractionator.  Now there is the proportionator. just as the optical fractionator reduces the work over the physical disector so does the proportionator reduce the work over the optical fractionator.

If a study requires only a week of counting then you may decide to skip learning about the proportionator. But, if the study requires hundreds or thousands of hours of counting then avoiding the proportionator is a bad idea.

The goal in all three methods
1. physical disector

2. optical fractionator

3. proportionator

is to obtain the correct answer. It is also important that the amount of work is not excessive.  The optical fractionator reduces the work by avoiding the needed to align two sections. The optical fractionator works in situations where the cells are well dispersed such as counting neurons. The optical fractionator fails in many dense tissues such as the liver where it is not possible to focus down through the tissue and obtain optical sections. The proportionator reduces the work by reducing the amount of counting that has to be done.

The basic idea behind the proportionator is that sampling does not always have to be with equal probability. The notion that all cells have to be sampled with equal probability to obtain an unbiased result is incorrect. What is correct is that if cells are sampled with equal probability, then an unbiased estimate is possible.


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