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99ejdea
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Aaaaaargh, dus ney1 kno how to do the inter quartile range and standard deviation???? help
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meepmeep
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(Original post by 99ejdea)
Aaaaaargh, dus ney1 kno how to do the inter quartile range and standard deviation???? help
Interquartile range is the range of the middle 50% of the data (eg. if your data was 1,3,5,9 then the interquartile range will be 3-5). Can be easily found by drawing a cummulative frequency graph.

To find the standard deviation, find the mean of the sample then takes this value away from each of the figures in the sample:

eg. if I had a sample of 1,2,3,4,5 the mean is 3, I will get:

-2,-1,0,1,2

Then square each of these figures to get rid of the negative numbers:
4,1,0,1,4

Add the lot together:
4+1+0+1+4=10
Then divide by the number of pieces of data (in this case, 5):
10/5=2

Then take the square root:
Square root of 2 = 1.414 (approx)

It's better if you set this out in a table with the headings:
Sample Sample minus mean sample minus mean squared

Then finding the total of the final column.

The formula is:

Standard deviation= Square root(sum of (samples - mean)^2/n) where n is the sample size.
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makesomenoise
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Interquartile range:

Find the median of your data. Then find the medians of the data either side of your median. Deduct the smaller data value from the larger. Bingo.
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meepmeep
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(Original post by XTinaA)
Interquartile range:

Find the median of your data. Then find the medians of the data either side of your median. Deduct the smaller data value from the larger. Bingo.
That's a clever quick way of doing it....
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makesomenoise
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(Original post by meepmeep)
That's a clever quick way of doing it....
<tips hat> I thank you good sir.
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zazy
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Interquartile range = upper quartile-lower quartile
upper quartile= 3(n+1)/4
Lower quartile=(n+1)/4
Standard deviation: the square roo t of variance
variance= The mean of the squared values - the mean squared
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