The Vascular Depression Subtype: Evidence of Internal Validity

BackgroundVascular depression has been proposed as a unique diagnostic subtype in late life, yet no study has evaluated whether the specified clinical features associated with the illness are jointly indicative of an underlying diagnostic class.MethodsWe applied latent class analysis to two independent clinical samples: the prospective, cohort design, Neurocognitive Outcomes of Depression in the Elderly (NCODE) study and the 8-week, multicenter, double blind, placebo-controlled Old-Old study.ResultsA two-class model consisting of vascular and nonvascular depressed patients provided an excellent fit to the data in both studies, χ2(6) = 2.02, p = .90 in the NCODE study and χ2(6) = 7.024, p = .32 in the Old-Old study. Although all of the proposed features of vascular depression were useful in identifying the illness, deep white matter lesion burden emerged with perfect sensitivity (1.00) and near-perfect specificity (.95), making it the only indicator necessary to determine class membership.ConclusionsThese findings, replicated across two independent clinical samples, provide the first support for the internal validity of vascular depression as a subtype of late-life depression.