OCR MEI Statistics 1

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Created by: Hopeful.Student
Created on: 26-04-18 18:47

S_xx. Step 1

Work out the mean. X bar = Summation of x divided by n.

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Step 2

Sum of the squares (S_xx) = Summation of (x-x bar)^2 = Summation of (x^2 - n (x bar)^2)

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Mean square deviation, MSD

S_xx/n = Summation of (x^2-n(x bar)^2)/n

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What is MSD for?

It gives an average of the distance of the points away from the mean. However, the #s we get are too big because we ^2 #s to make them +ve. Hence, we use RMSD.

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What is RMSD?

It is the root mean square deviation i.e. we square root the MSD.

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What is RMSD used for?

RMSD gives us a way to look at data and compare different sets of data. We want to RMSD if we are looking at a distinct set of numbers.

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The formula of RMSD.

((Summation of x^2-n*(x-bar)^2)/n)^1/2

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MSD and RMSD is for when we are looking at a large set of data. However, what if we get a small sample of data instead?

MSD and RMSD won't work if we use a mean of the sample for a good unbiased estimator. Instead, we will use a better unbiased estimator by instead /(n-1).

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Variance and standard deviation.

Variance=(Summation of x^2-n*(x-bar)^2)/(n-1) ; Standard deviation, s=((Summation of x^2-n*(x-bar)^2)/(n-1))^1/2

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What does standard deviation tell us?

It tells us how much (on average) the data deviates from the mean (the distance from the mean to the data point).

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The larger the standard deviation is... ;The lower the standard deviation...

...the more spread out the data is. ; ...the more consistent the data is.

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Another equation to identify outliers.

(x-bar)+2*s

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Other cards in this set

Card 2

Front

Step 2

Back

Sum of the squares (S_xx) = Summation of (x-x bar)^2 = Summation of (x^2 - n (x bar)^2)

Card 3

Front

Mean square deviation, MSD

Back

Card 4

Front

What is MSD for?

Back

Card 5

Front

What is RMSD?

Back

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OCR MEI Statistics 1