Research paperSeverity of complicated versus uncomplicated subthreshold depression: New evidence on the “Monotonicity Thesis” from the national comorbidity survey

•CsD includes one or more of six pathosuggestive features; UsD includes none.•Severity validators were suicidality, interference, seek help, hospitalized, GAD.•CsD is more severe than UsD and UMDD, and like CMDD, contrary to monotonicity.•A symptom count inadequately assesses subthreshold depression severity.•Complicatedness is superior to symptom count as a severity measure.

Background“Complicated” subthreshold depression (CsD) includes at least one of six pathosuggestive “complicated” symptoms: >6 months duration, marked role impairment, sense of worthlessness, suicidal ideation, psychotic ideation, and psychomotor retardation. “Uncomplicated” subthreshold depression (UsD) has no complicated features. Whereas studies show that complicated (CMDD) versus uncomplicated (UMDD) major depression differ substantially in severity and prognosis, UsD and CsD severity has not been previously compared. This study evaluates UsD and CsD pathology validator levels and examines whether the complicated/uncomplicated distinction offers incremental concurrent validity over the standard number-of-symptoms dimension as a depression severity measure.MethodsUsing nationally representative community data from the National Comorbidity Survey, seven depression lifetime history subgroups were identified: one MDD screener symptom (n=1432); UsD (n=430); CsD (n=611); UMDD (n=182); and CMDD with 5-6 symptoms (n=518), 7 symptoms (n=217), and 8-9 symptoms (n=291). Severity was evaluated using five concurrent pathology validators: suicide attempt, interference with life, help seeking, hospitalization, and generalized anxiety disorder.ResultsCsD validator levels are substantially higher than both UsD and UMDD levels, and similar to mild CMDD, disconfirming the “monotonicity thesis” that severity increase with symptom number. Complicated/uncomplicated status predicts severity, and when complicatedness is controlled, number of symptoms no longer predicts validator levels.LimitationsDiagnoses were based on respondents' fallible retrospective symptom reports during a lay-administered structured interview, which may not yield diagnoses comparable to clinicians' assessments.ConclusionCsD is more severe than UsD and comparable to mild MDD. Complicated status more validly indicates depression severity than the standard number-of-symptoms measure.