Spearman’s rank correlation coefficients between tissue-exclusive gene pairs, based on smooth quantile normalized data from GTEx. (a) False-positive associations are detected in qsmooth-normalized data between tissue-exclusive genes from different tissues, as can be seen in off-diagonal blocks of expression. (b) SNAIL removes most of these false-positive associations. (c) The receiver operator curve and (d) precision–recall curve, where the ground truth association between genes is defined by whether the genes share the same functional annotation in the STRING database.