Fleece Statistics Explained – the ‘CV’ Coefficient of variation.


The CV is a measure of dispersion from a given probability distribution – in most cases with fleece statistics a measure of the ‘normal’ distribution.

I have tried to confer over the following page or two that although the percentage CV may be higher than what is generally accepted to be good, a high % CV need not detract to heavily from a good or high quality fleece. Some examples below will hope to clarify.


Fleece Histogram Data 1;

14.9 Micron (we would all be happy with that!)

Standard Deviation (SD) is 4.14.

Therefore the CV is:

      

Fleece Histogram Data 2;

28 Micron (still o.k.)

Standard Deviation (SD) is 1.5.

Therefore the CV is:

Fleece 2 has a much more desirable CV, the CV highlights the uniformity and consistency in the fleece, however a high CV is not necessarily a bad thing. The variation in fleece 1 is greater but the fleece may have very few fibres overall over 19.04 microns suggesting a superior fleece.

When looking at a snapshot of fleece properties bear in mind the following, the SD of a normal population gives a good indication of where the majority of the fibres sit in that sample population. 1 SD in both directions from the sample mean will include ~ 68% of the data, 2 SD will include ~ 95% of the data and 3 SD will include ~ 99% of the data. Outside of 3 SD would be a rare occurrence.

As an example fleece 2 above would contain;

68% of its fibres in the range 26.5 - 29.5 microns
95% of its fibres in the range 25 – 31 microns.
99% of its fibres in the range 23.5 – 32.5 microns.

The data set for your particular fibre analysis will give a percentage over 30 microns rather than present the extreme value(s).

These figures are estimates based on the mean and dispersion of a theoretical fleece.

I hope this has helped!