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## negative correlation - how?

This topic has 2 expert replies and 6 member replies
kunalkulkarni Senior | Next Rank: 100 Posts
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Posted:
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#### negative correlation - how?

Sat Feb 09, 2013 5:23 pm
there are 2 sets of data:
X = {0,0,0,4,4,4,6,6,8}
Y = {50,38,56,34,32,42,28,34,29}
There is a negative correlation between X and Y.

Can anyone please explain me. how is the above statement true?
My understanding is as follows:
positive correlation - directly proportional
negative correlation - inversely proportional

Kunal

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mkdureja Senior | Next Rank: 100 Posts
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04 Jan 2013
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38 messages
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Thu Feb 14, 2013 12:55 am
As per my understanding, correlation is a statistical term with a proper formula. Its value varies from -1 to +1 for any set of data, with value of +1 representing perfect linear positive correlation (data set will draw a straight line in cartesian plane), similarly -1 represents a straight line with negative slope.
Basically, for any given set of data, even random, correlation will be either positive or negative, close to zero for highly uncorrelated/random data.
In the above question, it is clear that when X increases, Y decreases, other than for some exceptions, which can be ignored.

This is my understanding, open for other explanations.

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Tommy Wallach GMAT Instructor
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Thu Feb 14, 2013 9:31 am
Hey Mk,

While all that you said may be true, advanced statistics aren't really tested on the GMAT. So you don't need to know much other than a pure positive or a pure negative correlation (i.e. When X goes up, Y goes up; or when X goes down, Y goes up).

-t

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mkdureja Senior | Next Rank: 100 Posts
Joined
04 Jan 2013
Posted:
38 messages
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Thu Feb 14, 2013 12:55 am
As per my understanding, correlation is a statistical term with a proper formula. Its value varies from -1 to +1 for any set of data, with value of +1 representing perfect linear positive correlation (data set will draw a straight line in cartesian plane), similarly -1 represents a straight line with negative slope.
Basically, for any given set of data, even random, correlation will be either positive or negative, close to zero for highly uncorrelated/random data.
In the above question, it is clear that when X increases, Y decreases, other than for some exceptions, which can be ignored.

This is my understanding, open for other explanations.

### GMAT/MBA Expert

Tommy Wallach GMAT Instructor
Joined
21 Jan 2010
Posted:
451 messages
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Target GMAT Score:
800
GMAT Score:
770
Thu Feb 14, 2013 9:31 am
Hey Mk,

While all that you said may be true, advanced statistics aren't really tested on the GMAT. So you don't need to know much other than a pure positive or a pure negative correlation (i.e. When X goes up, Y goes up; or when X goes down, Y goes up).

-t

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ManhattanGMAT

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tabsang Senior | Next Rank: 100 Posts
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Tue Sep 17, 2013 9:14 pm
Hey Kunal,

Could you please elaborate on this.
I'm not quite sure that I got this

Cheers,
Taz

kunalkulkarni wrote:
Hey Hemant,
So the main catch is to find the transitioning numbers as X changes from 0 to 6. Just to ensure I understood it correctly, if below was the series for X and Y
0 - 50
0 - 38

4 - 42
4 - 36

6 - 32
6 - 40

then it would be impossible to find negative or positive correlation. right?

Thanks,
Kunal

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kunalkulkarni Senior | Next Rank: 100 Posts
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Posted:
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Sun Feb 10, 2013 11:38 pm
Thank you Hemant and Tommy. Appreciate your help.

Cheers,
Kunal

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Tommy Wallach GMAT Instructor
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Sun Feb 10, 2013 10:45 pm
Hey Kunal,

You are correct. In that set, there wouldn't be a correlation you could call either positive or negative.

-t

P.S. Indeed, BtG does not like white spaces in posts. It's a bit like trying to leave silence on your iPhone voice mail. Ever tried it? No dice.

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hemant_rajput Master | Next Rank: 500 Posts
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Sun Feb 10, 2013 8:34 pm
Hi Kunal,

I did some modification in pictorial representation in my previous post. I guess BTG post skips white space in forum. Hope this make it clear.

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