The lack of association between clinical and demographic factors and performance on the cognitive tests may partly reflect the homogeneity of the sample. People with BD, similar to those with unipolar depression, tend to have ECT somewhat later in the course of illness. Because we intentionally matched the non-ECT group to control for illness burden, we have an overall patient sample with established, recurrent illness. Thus, it is possible that, if patients had been more heterogeneous, we would have observed associations with past illness burden, such as those described using the CVLT in predominately euthymic populations