Finding a Central Value

2 Numbers

With just 2 numbers the answer is easy: go half-way between.

We can use that idea of “adding then dividing” when we have 3 or more numbers:

Notice that we divide by 3 because we have 3 numbers … very important!

So far we have been calculating the Mean (or the Average):

Mean: Add up the numbers and divide by how many numbers.

But sometimes the Mean can let you down:

The Mean was accurate, but in this case it was not useful.

But you could also use the Median: simply list all numbers in order and choose the middle one:

List the ages in order:

Sometimes there are two middle numbers. Just average those two:

The Mode is the value that occurs most often:

How to remember? Think “mode is most”

But Mode can be tricky, there can sometimes be more than one Mode.

When there are two modes it is called “bimodal”, when there are three or more modes we call it “multimodal”.

Outliers are values that “lie outside” the other values.

They can change the mean a lot, so we can either not use them (and say so) or use the median or mode instead.

The mean (average) we have been looking at is more correctly called the Arithmetic Mean.

There are other types of mean! Here are two examples:

The Geometric Mean multiplies the numbers together, then does a square root or cube root etc depending on how many numbers, like in this example:

The Harmonic Mean adds up “1 divided by number” then flips it like this:

Mean, Median and Mode are the most common ways of measuring central value, but there are other ways.

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