To review, correlation measures the relationship between two sets of data.

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Historically there has been little correlation between the dollar and oil prices, and while the relationship strengthened last year following the credit crisis, it has since weakened again.

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This was an observational study of roughly 16, 000 women, so it was not able to establish a cause and effect relationship between taking the supplements and death, but the correlation was significant.

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He argues that the negative correlation between the greenback and corporate earnings is clear, but the far stronger relationship is between profits and unit sales growth, which is more closely-tied to economic output.

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While the study did indeed identify a striking correlation, researchers were unclear what actually drove this cause-and-effect relationship, with skeptics pointing out that a number of factors may have caused this link which were uncontrolled for in the study.

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There was still a negative correlation between the size of the national debt and GDP growth, but there was no implied causal relationship or sudden change at 90 percent.

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