Michael Morgan, an experimental psychologist at Sussex University, admits that there are holes in the experimental record that need to be filled before the link between the drug and nasty long-term effects moves from correlation to causation.

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Although he cannot definitely rule out a direct effect by the pollution on the birds' metabolism of the yellow pigment, or its incorporation into their feathers, the correlation between a shortage of caterpillars and faded plumage is strong evidence of a link between pollution, diet and bird colour.

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The study found there was a positive link between good information technology and national test results, of 0.07 under the Spearman Rank Correlation statistical measurement system.

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