Morphometricity is Biased by Image Smoothness

COEX 

Morphometricity is the proportion of phenotypic variation that can be explained by macroscopic brain morphology. It is estimated in a manner similar to heritability, with intersubject similarity of brain images replacing genetic relatedness [4]. It provides a simple approach to summarize the link between a phenotype and high-dimensional brain data with a single value. However, recent results have found unexpectedly large morphometricity values, e.g. brain structure explaining over 90% variation in BMI [2]. In this work we explore the role of smoothness in morphometricity in theory, simulation and real data evaluations, showing that image smoothness induces a positive bias that can help explain these unusual results.