[Correlations--How to measure non-directional empirical associations between medical parameters, and how to present them in a correct and illustrative manner].
While directional relationships (e.g., cause-effect relations) should be described by regression models, symmetrical associations between medical parameters are addressed adequately by correlation measures. The choice of the appropriate correlation measure should depend on the type of scale and the distributional assumptions. In publications the employed correlation measures should be clearly stated, and their values should be reported with confidence limits rather than p values.Correlations just describe associations but on their own do not allow conclusions on causes of associations. They are extremely vulnerable for misinterpretations, since basically different mechanisms can produce similar correlation coefficients. More information can be received by looking at the underlying scattergrams.The simultaneous analysis of more than two variables requires multivariate statistical techniques and should not be attempted without professional help.
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