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# how to determine co-relation between two sets?

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Manager
Joined: 23 Aug 2011
Posts: 76
how to determine co-relation between two sets?  [#permalink]

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18 Nov 2012, 03:20
Is the corelation positive, negative, Strongly positive,Strongly negative? Is there any solid quantifier by which we can differntiae betwen a strongly (+/-) and a regular +/- co-relation?
Thanks.

I am posting one table from gmatprep, what is the co-relation between the two columns viz. b/w no of lanes and avg customer age.?
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Joined: 22 Sep 2012
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Re: how to determine co-relation between two sets?  [#permalink]

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03 Dec 2012, 03:20
I took this test too. The answer is "negative correlation...", but I don't understand how
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Joined: 23 Nov 2012
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Concentration: Finance, Economics
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Re: how to determine co-relation between two sets?  [#permalink]

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03 Dec 2012, 09:22
The easy way to remember is:

If, in average, x goes up/is high and y goes up/is high => positive corr
If, in average, x goes up/is high and y goes down/is low=> negative corr
and vice versa
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Re: how to determine co-relation between two sets?  [#permalink]

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04 Dec 2012, 00:29
I think we can explain the answer like this:

3 stores with 0 self-check lane, and the average customer ages are 50.50, 38.80, 56.70 respectively.

-> So: 0 lane - (50.50 + 38.80 + 56.70)/3 = 48.66 average age

3 stores with 4 self-check lanes, and the average customer ages are 34.50, 32.00, 42.50 respectively.

-> So: 4 lanes - (34.50 + 32.00 + 42.50)/3 = 36.33 average age

2 stores with 6 self-check lanes, and the average customer ages are 28.40 and 34.60 respectively.

-> So: 6 lanes ; (28.40 + 34.60)/2 = 31.5 average age

1 store with 8 self-check lanes, and the average customer ages is 29.90

--> negative correlation.
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Re: how to determine co-relation between two sets?  [#permalink]

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07 Dec 2012, 05:42
Well the answer is indeed negative correlation. We can follow this approach to conclude whether correlation is +/- or null. Since # of lanes is already arranged in ascending order, you may roughly draw a line graph per the Average customer age values on scratch paper as shown in the image below.

Now next step is to visualize a trend line. The given trend line descends from Top right hand quadrant to bottom left hand quadrant. This means when the values of # of lanes are rising, the corresponding Average customer age values are decreasing, hence a case of negative correlation.

e-GMAT has launched 15+ hours of interactive audio visual content on IR. IR questions that are true reflection of Official Guide questions. It encompasses 35 concepts, 120+ original questions, and 2 full length Mock Tests.

Should you wish to see couple of questions on correlation with an interactive audio-visual solutions, pl. visit e-GMAT free trial.

-Best Regards!

Shalabh Jain
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Re: how to determine co-relation between two sets? &nbs [#permalink] 07 Dec 2012, 05:42
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