Estimating variance

Posted in Maths, Statistics 2

You can estimate the variance of a population from a sample of a population by using the following equation:

$Dynamic image 0$

This can also be written as:

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Where n the number in the sample and $Dynamic image 2$ is the sample mean.

Estimate the variance of the test scores for pupils in a school based on the following sample:

Student	A	B	C	D
Results	90	89	77	56

First calculate the sample mean:

$Dynamic image 3$

Next calculate the sum of the scares of the values:

Student	A	B	C	D	Sum
Results squared	8100	7921	5929	3136	25086

Next, plug in the values into the equation:

$Dynamic image 4$

A level revision