To the Editor The article by Kraguljac and colleagues1 presents a potentially important finding on the association between hippocampal glutamate levels and hippocampal morphology. However, one aspect of the article requires correction. The authors report a significant positive correlation (r = +0.39) between N-acetylaspartate (NAA)/creatine (Cr) and glutamate and glutamine (Glx)/Cr in normal participants that is lost in patients with schizophrenia (r = −0.19). Unfortunately, using zero correlation as the null hypothesis here is incorrect because Glx/Cr and NAA/Cr are not independent numbers. Both include the Cr value in their denominator.
Maddock R. The Problem of Spurious Correlations Between Pairs of Brain Metabolite Values Measured in the Same Voxel With Magnetic Resonance Spectroscopy. JAMA Psychiatry. 2014;71(3):338-339. doi:10.1001/jamapsychiatry.2013.4343