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In Reply Dr Maddock’s letter in response to our recent article1 suggests that it is statistically problematic to report correlations between ratios without accounting for spurious correlations. Spurious correlations were first described by Pearson, who showed that correlations between 2 ratio variables that have the same denominator may be present, even when the original variables from which the ratios were derived are uncorrelated.2
Kraguljac NV, Cutter GR, Morgan C, Lahti AC. The Problem of Spurious Correlations Between Pairs of Brain Metabolite Values Measured in the Same Voxel With Magnetic Resonance Spectroscopy—Reply. JAMA Psychiatry. 2014;71(3):339-340. doi:10.1001/jamapsychiatry.2014.22