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## Vanessa Mu

on 12 August 2014

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#### Transcript of measures of spread

mean & variance
A coin is tossed 4 times.
How many heads would you expect to get,on average.
the expected value is a way of estimating the mean without resorting to actual experiments.
You would expect to get a head about half of the time
we expect
1
---- * 4=2
2
Standard Deviation
The range is the difference between the highest and lowest scores in a data set and is the simplest measure of spread. So we calculate range as:
The standard deviation is a measure of the spread of scores within a set of data
The population standard deviation formula is
= population standard deviation
= sum of...
= population mean
= number of scores in sample
we write the expectation of X as E(X)
Range
Range = maximum value - minimum value
For example, let us consider the following data set:

23 56 45 65 59 55 62 54 85 25
What is the range?
The standard deviation is a measure of the spread of scores within a set of data. Usually, we are interested in the standard deviation of a population. However, as we are often presented with data from a sample only, we can estimate the population standard deviation from a sample standard deviation. These two standard deviations - sample and population standard deviations - are calculated differently. In statistics, we are usually presented with having to calculate sample standard deviations, and so this is what this article will focus on, although the formula for a population standard deviation will also be shown.

The maximum value is 85 and the minimum value is 23. This results in a range of 62, which is 85 minus 23
maximum value :85
minimum value: 23
85 - 23 = 62
So the range is 62