My Math Forum Is This Correlation Possible?

 November 3rd, 2014, 05:21 AM #1 Senior Member   Joined: Oct 2013 From: New York, USA Posts: 549 Thanks: 78 Is This Correlation Possible? I made a regression equation with three independent variables and one dependent variable. Two of the independent variables had a positive coefficient (positive correlation) with the dependent variable and one independent variable had a negative coefficient. Then when I made a regression equation with that independent variable as the only independent variable, it had a positive coefficient with the same dependent variable. Is it possible for two variables to have a positive correlation on their own but appear to have a negative correlation when more independent variables are added in?
 November 3rd, 2014, 06:53 AM #2 Math Team   Joined: Dec 2013 From: Colombia Posts: 6,941 Thanks: 2267 Math Focus: Mainly analysis and algebra I'm reasonably sure that the answer is 'yes'. I think you might be talking about Simpson's paradox. Last edited by v8archie; November 3rd, 2014 at 06:57 AM.
November 3rd, 2014, 12:08 PM   #3
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Quote:
 Originally Posted by v8archie I'm reasonably sure that the answer is 'yes'. I think you might be talking about Simpson's paradox.
I don't think my question is in that category. Simpson's Paradox involves two variable individual vs. combined, with the same amount of variables examined both times. I have one equation with four variables and one equation with two variables. Call them a, b, c, and x, with three independent variables and x being the dependent variable.

Equation 1 used every variable and:
a and x had a positive correlation
b and x had a negative correlation
c and x had a positive correlation

Equation 2 had only b and x and in that case b and x had a positive correlation. Is that possible?

 November 3rd, 2014, 01:15 PM #4 Math Team   Joined: Dec 2013 From: Colombia Posts: 6,941 Thanks: 2267 Math Focus: Mainly analysis and algebra Maybe the same amount of variables each time, butthe different environments equate to other variables having differing values, perhaps uncontrolled, or perhaps controlled unintentionally. Thanks from EvanJ
June 9th, 2017, 05:20 PM   #5
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Quote:
 Originally Posted by v8archie I'm reasonably sure that the answer is 'yes'. I think you might be talking about Simpson's paradox.
Over 2.5 years later, I looked farther down that page after skipjack linked to it another topic. What I said is a type of Simpson's paradox.

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