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  • Meg Simpson

Don't be mean.... why averages don't always tell the whole story.

Does giving an average (mean) always tell the whole story we want them to tell?


Someone once told me that if a 20 year old and a 80 year old start dating, the average age of the relationship is 50, but that doesn't make it okay, or socially acceptable (nor does it fit the half your age plus seven rule!).


As a quick flashback to primary school maths classes and keeping it pretty simple, there are three main types of averages.

Mean - this is what most people mean when they say average, its the total of all numbers divided by the number in the list

Median - The middle number

Mode - The most common number.

And then also the ever important Range - the spread of numbers.


But where does this fit into our farming systems?


The couple of key ones that stand out for me and discussions I regularly have with farmers is around herd body condition scores, dairy heifer and beef live weights and milk production statistics.


Take the body condition score for these two farms for example:

Both farms have a herd body condition score mean of 4.20. As an average pre-mating we may be pretty happy about where this is at, but what does it actually represent for these herds?


Farm One has 51% of cows at a body condition score of 4.0 or less.

Farm Two has 63% of cows at a body condition score of 4.0 or less.


Farm One has 6% of cows at a body condition score of 5.0 or above.

Farm two has 18% of cows at a body condition score of 5.0 or above.


The management decisions that would be made for these two farms would be very different once we consider the range of the herd and the actions required for the individual animals/groups of animals.

Or how about these three bull mobs, that all have a mean weight of 250kg.



Mob B has a nice tight spread, with the range between all animals in the mob being just 45kg, as opposed to Mob C which has the heaviest animal being just 10kg off being twice the weight of the lightest one - a massive range of 160kg!


The management of individuals and sub-sets as well as a good understanding of the range within a mob is always more important than making sure the average ticks the box of the "target". Put simply, if our "average" is at target that usually means there is a large proportion of the mob that is below the target.

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