Understanding the Histogram

It is impossible to talk about histograms without putting them into the proper context. A histogram is a tool for evaluating Alpaca fiber at a given point in time.  This tool must be used as part of an assessment protocol that includes  a number of other criteria to evaluate the fiber of any individual animal.

What we hope to do here is provide a very basic, but thorough, outline of how to understand a histogram and put it into the proper context with the other evaluating factors so that you can make decisions about Alpaca fiber with more information and confidence.

What is a Histogram? 

A histogram is a graphical representation of a set of data. There are now several types of testing that are represented in histograms that look very different.

  • OFDA – Optical Fiber Diameter Analysis
  • Laserscan – End Cut Laser scanning

Laserscan

A Laserscan histogram represents the data from a 2” X 2” sample of fiber, usually from the mid -side of an alpaca.  Some breeders will take multiple samples from shoulder, hip and mid-side.  This is called Grid Sampling.  In a Grid Sample, all of the samples are tested and the results averaged. The standard sample is cut as close to the skin as possible and the cut end of the fiber is evaluated. This is important because it is the most recent growth and best represents the current environmental factors in the Alpaca’s growth such as diet, stress, pregnancy and lactation. The sample of fiber is scanned by a laser device  which measures each fiber diameter and then plots that data into a histogram.

OFDA

An OFDA report contains two elements; a histogram and an historical evaluation chart.

In this type of testing both the end cut and the entire length are tested. Fiber samples taken even an inch above the skin can give a very different set of data because of varying factors that affect the alpaca throughout the year. Using OFDA, fiber samples are tested along the entire length of the staple which provides a set of data representing an entire years growth.

How to read a Histogram

Look at the graph table.  The fiber diameters are listed on the horizontal axis (across the bottom). The number of fibers is listed as a percentage of the whole sample on the vertical axis (Left side).   Be aware that the numbers across the bottom will be a slightly different range on each histogram based on the highest micron detected in the sample.  Some graphs will range from 4 to 40 microns and others will range from 4 to 55 or 65 microns.

When you view the bell curve of data you look for a tight grouping with fiber size variations no more than 3-5 microns off the average fiber diameter. You also want to be aware of the highest microns detected so that you can put the bell curve into perspective.  Also remember to read the Age, Sex, Color and date sample taken as they are all important factors in the evaluation of the fiber.

Histogram Terminology Explained

Micron
A micron is 1/1000 of a millimeter.  A human hair ranges from about 60 to 90 microns in diameter so imagine fibers 1/1000 the diameter of one of your hairs. Obviously this is a very fine fiber and would be incredibly difficult to detect differences using only ones sense of touch. I have met two breeders who can take a few Alpaca fibers between their fingers and correctly determine the micron but this is a very rare occurrence. Histograms give us an accurate way to measure this diameter.
AFD (Average Fiber Diameter)
Exactly what it says.  The fiber sample is scanned and the number of fibers of each micron are counted.  The Average Fiber diameter will be the total microns combined divided by the total number of fibers counted.

Example:

Sample Analysis:

 3 fibers X 15 microns = 45 microns

 3 fibers X 16 microns = 48 microns

 20 fibers X 18 microns = 360 microns

 20 fibers X 21 microns = 420 microns

 20 fibers X 24 microns = 480 microns

Total Fibers - 3+3+20+20+20 = 66 fibers measured

Total Microns - 45+48+360+420+480 = 1,353 total microns measured

Final Equation - 1,353 divided by 66 = 20.5 Average Fiber Diameter

SD (Standard Deviation)
A term which represents an average of individual deviations (stated in plus or minus micron values) from the Average Fiber Diameter. In other words the amount of deviation between each individual fiber’s diameter and the Average Fiber diameter. 

Example:

If the AFD = 20.5 then another average is calculated  using an equation that determines the distance of each fiber in the sample, in microns, from 20.5 microns.  As I recall from my college days in statistics, the equation is about 4 feet long and requires several calculators and a couple of pencils to figure it out.  I will leave that to the computers.  But if we use the same grouping that we used for our example of Average Fiber Diameter you can easily see that none of the micron counts is more than 5.5 microns away from the AFD of 20.5.   You can surmise that the Standard Deviation for this particular sample would be quite low.

The bell curve on a sample with a good Standard Deviation will have a very close grouping that is tall and narrow meaning that the fibers in the sample are not that far off the average.  The smaller the Standard Deviation, the more uniform in diameter is the sample.

CV (Co-efficient of Variation)
The Standard Deviation divided by the Average Fiber Diameter, multiplied by 100 and reported as a percentage. 

Example 1.

A.  Standard Deviation  - 4.1, Average Fiber Diameter – 21.4

                   4.1 / 21.4 = .192 X 100 = CV 19.2%

            B.   Standard Deviation – 4.2, Average Fiber Diameter – 25.9

                  4.2/ 25.9 = .161 X 100 = CV 16.1%

In the above example, equation B would mathematically be the more uniform fleece.

But don’t let math be your only guide.  Compare equation B with equation C

Example 2.

B.   Standard Deviation – 4.2, Average Fiber Diameter – 25.9

                  4.2/ 25.9 = .161 X 100 = CV 16.1%

C.   Standard Deviation – 8.4, Average Fiber Diameter – 51.8

                  8.4/ 51.8 = .162 X 100 = CV 16.2%

the CV in these two equations is almost identical but you would definitely feel a difference between an animal that had an AFD of 25.9 and one that was 51.8.

This CV is a very mathematical way of saying that you want to compare two different things.  The CV is most useful when comparing two separate fleeces.  If the fleeces have he same Standard Deviation and one has a higher Average Fiber Diameter. Mathematically, the fleece with the higher Average Fiber Diameter is the more uniform fleece. 

What the numbers infer is that if you take this sample and apply it to the entire area of fleece you would have more uniform characteristics. When comparing two fleeces the CV is a more useful measure of uniformity of the entire fleece.  You want a minimum amount of variation throughout a fleece so the lower the CV, the better.

Fibers over 30 Micron
This measurement shows the coarse edge that effects what the fiber will be used for.  If the percentage number of fibers over 30 micron is very high in a sample, the fleece will have a higher “prickle” factor that we associate with strong fibers.

If we use the examples from our CV calculations and apply the fibers over 30 micron information the picture changes drastically.

Example

A.  Standard Deviation  - 4.1, Average Fiber Diameter – 21.4

            Co-efficient of Variation -  19.2%, Fibers over 30 Micron - 2.6%

B.   Standard Deviation – 4.2, Average Fiber Diameter – 25.9

            Co-efficient of Variation  -16.1%, Fibers over 30 Micron  -13.1%

C.   Standard Deviation – 8.4, Average Fiber Diameter – 51.8

            Co-efficient of Variation  -16.2%, Fibers over 30 Micron – 27%

Sample A Would be the overall finest fleece with the lowest “Prickle factor, Sample B would be the easiest to process commercially because of it’s uniformity and Sample C would be rug fiber based on it’s over 30 Micron percentage.

CF: Comfort Factor
The percentage of fibers under 30 microns.   100% comfort factor would represent that all the fibers in the sample were under 30 microns. 70% comfort factor would represent that 30% of the fibers in the sample were over 30 microns.  This term has shown up in the last year or so and seems to be directed more toward marketing terminology than scientific terminology

CRV: Curve or Fiber Curvature
Another new measurement that gives the average curvature of all the fibers in a sample.  It is specifically a measurement for Huacaya fleece as Suri has very little curve.  It measures degrees of curve per one millimeter of fleece length.  A higher CRV would represent a deeper crimp in Huacaya fiber.

Again, you have to put all the pieces together to form the big picture. The pieces of a histogram form a single indicator in the evaluation of alpaca fiber.  It is important to remember that the histogram needs to be used in conjunction with other subjective and objective factors in determining fleece quality.  The following glossary of terms is important to understand the entire fiber picture from both the processor and producer’s perspective.

Objective Criteria

Can be definitively and scientifically measured.
Staple Length
The length of the fibers in a sample from end to end.  When we refer to staple length we are talking about the length of the fiber.  In Huacaya this is usually the length after one year of growth.  In Suri it could be anywhere from one to three years growth.  Commercial processors use staple of 6 mm or about 3.5 inches, anything longer than that is cut to size.  For hand spinners, the longer the staple the better because it makes it easier to spin together.  Again, you have to remember the end use of the fiber.
Tensile Strength
The measurement of a fiber’s strength before it snaps under pulling pressure.  Fiber affected by poor nutrition or poor health will break easily.  If you shear 12 pounds of fiber off an animal but it cannot withstand the rigors of processing or normal human use then the fiber is not very useful and will not have a very high value.
Fleece Weight

The weight of fiber sheared from an animal.  Usually divided into blanket and neck and leg fiber and weighed separately.  Average weight of a fleece is currently 4-6 pounds per year.  Increased fleece weight is one of the areas that breeders are currently working on.  Note that the same weight in Suri fiber will have much less volume because of the locking character of the fleece.
Subjective Criteria
Cannot be measured by machine.  These items are measured by the experienced eye and hand of the sorter and breeder. 
Crimp
The wave created by the two parts of a fiber twisting around each other. The  paracortex and  orthocortex are parts of each individual fiber and they create crimp. The debate on crimp could go on for days.  Some think it is important, some do not.  Put simply, if you have a crimpy fiber it stretches out to a longer staple length and it allows more fibers to fit into a square inch of fleece which equates to density.  A fleece with good crimp is denser and produces more fleece from a single animal.
Density
The number of hair follicles per square inch on an animal.  Primary follicles are the guard hairs or medulated fiber.  Secondary follicles surround each primary follicle.  The more secondary follicles, the denser the fleece.  Density can be measured by skin sampling but is not a practice commonly used in the North American Alpaca industry.  It will become more widely used as the industry grows. 
Handle
The feel of a fiber.  Softness in Huacaya and Silkiness or slick feel in Suri.
Luster
The shine or brightness usually associated with Suri fleece.  Caused by higher reflectivity of locks and the longer scale length in suri fiber.  Huacaya fleece will have “brightness” rather than true luster but it is a developing element.
Color
In a production environment a uniform color throughout the blanket reduces the need for sorting and separating — saving time and making processing easier.
Uniformity
Refers to even distribution of all the characteristics that are valued in a fleece: Diameter or Fineness, Color, Staple Length, Crimp, Density, Handle and Tensile Strength.  If all these factors are the same at the shoulder as they are on the hip then you have uniformity.

How important are these objective criteria in evaluating the fleece quality?

The Michell Company, the largest processor of alpaca fiber in the world, uses Peruvian Quechua Indian women to sort their fiber for color and fineness.  While they do test some batches, they believe that there is no better process for evaluating all the factors of a fleece than the practiced human hands of these women who have been sorting fiber for generations and generations.  To evaluate a fleece without these criteria would be a costly mistake.

Several very important pieces of information are not on any graph but they provide perspective for anyone reading a histogram.  Remember to read the Age, Sex, Color and date sample taken as they are all important factors in the evaluation of the fiber.

Age

A study done by B.A. McGregor and K. L. Butler for Primary Industries Research in Victoria, Australia shows that age is an important variable in fleece Micron.  Fleeces from animals at 1.5 to 2 years of age compared with the same animals at 4 to 7 years of age showed significant increase in mean fiber diameter.  They state that “Sampling alpacas at under 2 years of age is likely to substantially decrease selection efficiency for lifetime fibre(sic) diameter attributes.”  Cria fleece will always be the finest fleece because it has not been affected by nutrition, hormones or outside stresses.  The best time to get a real picture of the lasting power of fleece genetics would be at age 2 or 3.

Sex

No significant difference is seen between male and female fleeces until maturity.  At this point hormones will play a large role.  A breeding male will be subject to higher levels of testosterone and a breeding female will be subject to varying levels of progesterone.  Both these hormones will impact mean fiber diameter.  So, if you are looking at a histogram of an 8 year old female who has had multiple cria you will most likely see a much higher AFD than a maiden female.

Color

For the last twenty years breeders in the United States have been breeding alpacas with color in mind.  We love the natural colors in this fabulous fleece.  However, in Peru, for 70 years before the U.S. ever heard of alpacas, they bred mainly white because that is what was commercially efficient.  So the white alpaca has had a great deal more development time than the color.  White fleece will most often be the finest, with the best structure because of years and years of breeding white.  Colored fleece has a long way to go to match the statistics of white fleece.  When you read a histogram, be aware of the color of the animal for perspective.
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