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2. http://en.wikipedia.org/wiki/Correlation_and_dependence
3. Croxton FE, Cowden DJ, Klein S (1968) Applied general statistics. Pitman, London, p 625
4. Dietrich CF (1991) Uncertainty, calibration, and probability: the statistics of scientific and industrial measurement. Inst of Physics Pub, London, p 331
5. Aitken AC (1936) Statistical mathematics. Oliver and Boyd, Edinburgh, p 95