Variations in Fibre Diameter - Understanding Distribution Histograms

Why use a histogram?

A histogram is a graph which shows the individual fibre diameter measurements of a fleece sample.

• The fibre diameter of each fibre is recorded on the graph.
• The fibre readings are put into ‘ bars’ on the chart, usually in one micron groups.
• The higher the height of the ‘ bar’ , the more fibres have been measured in that micron group.

The histogram is a quick, easy way to view the variability of fibre diameter within a sample.

Below is an example of a histogram

Some tips when using histograms

Histograms can provide a useful overview of the sample, but in practice the summary statistics (Mean Fibre Diameter, Standard Deviation of Diameter, Coefficient of Variation of Diameter & Comfort Factor) are the most used and useful way of conveying information on the fleece sample.

Compare the adjacent three histograms - which fleece sample is best?

The answer is they are all the same set of results, presented using different scales on each graph.

When comparing histograms:

• check that the scale used on each graph is the same.
• preferably use a graph which has the % of fibres on the vertical axis.

Quite often, people try to make judgments on graphs with different scales. Even disregarding the value of such judgments, whether a graph looks "pointy" or "flat" has more to do with the scale used on the graph than the sheep in question.

Histograms derived from individual animals will usually be more meaningful than those derived from farm lots. This is simply because the variation in Mean Fibre Diameter for individual animals within the same mob will be larger than between the classed lines produced from the mob.

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FURTHER INFORMATION

Ian Ashman
General Manager Customer Relations
AWTA Ltd
Ph: 03 9371 4103
Fax: 03 9371 4191
Email: ian.ashman@awta.com.au