Standard-Deviation gcse Edexcel

Standard Deviation

What is the standard deviation of a data set?

• The standard deviation of a data set is a measure of dispersion (i.e. a measure of spread)

  • It measures how the data is spread out relative to the mean

    • If the standard deviation is small then most data values are close to the mean

    • If the standard deviation is large then many data values will be further away from the mean

  • If the data has units (seconds, cm, etc.), then the standard deviation has the same units as the values in the data set.

• The Greek letter (lower case sigma) is often used for standard deviation

How do I calculate the standard deviation for a data set?

• There are two different formulas you can use to calculate the standard deviation

  • Usually the second formula will be the quickest one to use

    • But make sure you know how to use both of them

• 

  • In this formula:

    • is the number of values in the data set

    • is the mean of the data set

    • is ‘any value‘ in the data set

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