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Standard Deviation

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Joined: 09 Mar 2016
Posts: 1287
Standard Deviation  [#permalink]

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New post 18 Apr 2018, 07:43

Standard Deviation



Standard deviation is a statistical measurement of the variation in a set of data. Standard deviation indicates how much the values of a certain data set differ from the mean on average. In a normal distribution -- where data is roughly equally distributed -- about 68 percent of data points lie within one standard deviation of the mean and 95 percent of values lie within two standard deviations of the mean.

For example, if the mean score on a certain standardized test is 1,200 and the standard deviation of scores is 100, you would expect 95 percent of test takers to get a score within two standard deviations of the mean, or between 1,000 and 1,400.

I have question regarding the above example can someone explain visually :) why between 1000 and 1400 and NOT 1100 and 1300 ?

many thanks :)

D.
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Re: Standard Deviation  [#permalink]

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New post 18 Apr 2018, 08:48
1
The rule to understand in this type of question is what I will call the 68-95-99.7 rule:

In a normal distribution - 68% of the values will lie within +/- 1 SD of the mean. 95% of the values will lie within +/- 2D, and 99.7% of the values will lie within +/- 3 SD of the mean.

- ice
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Re: Standard Deviation &nbs [#permalink] 18 Apr 2018, 08:48
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