Granger causality model inference.

Comparison of A) Do any of the lymphocyte populations Granger-cause viral load? The Deviance Information Criterion (DIC) of the simplest model (past viral load predicts future viral load) was compared with the DIC of alternative models in which past viral load and a range of different lymphocyte populations (alone or in combination as specified in the table) were predictors of future viral load. B) Does viral load Granger-cause the lymphocyte populations? The analysis was reversed and the DIC of the listed models is compared with the DIC of models including only one of the lymphocyte populations as predictor (i.e. without viral load). ΔDIC is defined as DIC of the simplest model minus the DIC of the more complex model. As a rule of thumb we consider strong support for the simplest model when ΔDIC is 10 [90]. Vt: viral load at time t. Tt: CD4+ T cells at time t. CD8t: CD8+ T cells at time t. NKt: NK cells at time t. Bt: B cells at time t. The only model to show a large improvement over the simplest model with past viral load only was a model with past CD8+ T cells and target cells (in bold above).