title: Quantifying colocalization by correlation: the Pearson correlation coefficient is superior to the Mander's overlap coefficient.
abstract: The Pearson correlation coefficient (PCC) and the Mander's overlap coefficient (MOC) are used to quantify the degree of colocalization between fluorophores. The MOC was introduced to overcome perceived problems with the PCC. The two coefficients are mathematically similar, differing in the use of either the absolute intensities (MOC) or of the deviation from the mean (PCC). A range of correlated datasets, which extend to the limits of the PCC, only evoked a limited response from the MOC. The PCC is unaffected by changes to the offset while the MOC increases when the offset is positive. Both coefficients are independent of gain. The MOC is a confusing hybrid measurement, that combines correlation with a heavily weighted form of co-occurrence, favors high intensity combinations, downplays combinations in which either or both intensities are low and ignores blank pixels. The PCC only measures correlation. A surprising finding was that the addition of a second uncorrelated population can substantially increase the measured correlation, demonstrating the importance of excluding background pixels. Overall, since the MOC is unresponsive to substantial changes in the data and is hard to interpret, it is neither an alternative to nor a useful substitute for the PCC. The MOC is not suitable for making measurements of colocalization either by correlation or co-occurrence.
authors.affiliation: The Wenner-Gren Institute, Stockholm University, 106 91 Stockholm, Sweden.
authors.forename: Jeremy
authors.initials: J
authors.lastname: Adler
authors.forename: Ingela
authors.initials: I
authors.lastname: Parmryd
mesh_terms: D002477:Cells / Q000378:metabolism; D005456:Fluorescent Dyes / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D018709:Statistics, Nonparametric
chemical_list: D005456:Fluorescent Dyes