69: Addressing Group Effects In The SPICE Test For Intermodal Correspondence

Thomas M. Menino Convention & Exhibition Center 

The simple permutation-based inter-modal correspondence (SPICE) test is commonly used to test for intermodal correspondence, i.e., coupling between brain features obtained from different imaging modalities. It tests for the null hypothesis that the distribution of intermodal correspondence within a subject is no different than that between subjects. Implemented as a permutation test, SPICE assumes that subjects are exchangeable under the null. However, it is known that many neuroimaging findings vary with development, sex, or disease state. In this work, we set out to understand how additional covariates impact the results of SPICE. Using neuroimaging data from the Philadelphia Neurodevelopmental Cohort and simulated data, we identify a problem with SPICE analogous to "Simpson's paradox", wherein the results are confounded by group effects. We demonstrate how naive analyses may lead to confusing or improper results. We propose and evaluate two approaches for performing SPICE that account for measured confounding: (1) restricted permutations; (2) Fisher's method. Our results represent an important evaluation and extension of SPICE that increases its rigor and generalizability.

Neuroimaging

Nonparametric

Hypothesis testing 

Section on Statistics in Imaging