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Statistics Index

• Basic concepts:


The mean is just the average of the numbers.

It is easy to calculate: add up all the numbers, then divide by how many numbers there are.


The Median is the "middle number" (in a sorted list of numbers).

To find the Median, place the numbers you are given in value order and find the middle number.


The mode is simply the number which appears most often.

To find the mode, or modal value, first put the numbers in order, then count how many of each number.

This makes it easy to see which numbers appear most often.

standard deviation,

Deviation just means how far from the normal

The Standard Deviation is a measure of how spread out numbers are.

Its symbol is σ (the greek letter sigma)

The formula is easy: it is the square root of the Variance.


The Variance is defined as the average of the squared differences from the Mean.

To calculate the variance follow these steps:

    • Work out the Mean (the simple average of the numbers)
    • Then for each number: subtract the Mean and square the result (the squared difference).
    • Then work out the average of those squared differences.