Problematic assumptions have slowed down depression research: why symptoms, not syndromes are the way forward

Abstract

Major depression (MD) is a highly heterogeneous diagnostic category. Diverse symptoms such as sad mood, anhedonia, and fatigue are routinely added to an unweighted sum-score, and cutoffs are used to distinguish between depressed participants and healthy controls. Researchers then investigate outcome variables like MD risk factors, biomarkers, and treatment response in such samples. These practices presuppose that (1) depression is a discrete condition, and that (2) symptoms are interchangeable indicators of this latent disorder. Here I review these two assumptions, elucidate their historical roots, show how deeply engrained they are in psychological and psychiatric research, and document that they contrast with evidence. Depression is not a consistent syndrome with clearly demarcated boundaries, and depression symptoms are not interchangeable indicators of an underlying disorder. Current research practices lump individuals with very different problems into one category, which has contributed to the remarkably slow progress in key research domains such as the development of efficacious antidepressants or the identification of biomarkers for depression. The recently proposed network framework offers an alternative to the problematic assumptions. MD is not understood as a distinct condition, but as heterogeneous symptom cluster that substantially overlaps with other syndromes such as anxiety disorders. MD is not framed as an underlying disease with a number of equivalent indicators, but as a network of symptoms that have direct causal influence on each other: insomnia can cause fatigue which then triggers concentration and psychomotor problems. This approach offers new opportunities for constructing an empirically based classification system and has broad implications for future research.

Measuring depression over time . . . Or not? Lack of unidimensionality and longitudinal measurement invariance in four common rating scales of depression.

“…If we spread 10 thermometers (the indicators) across a large hall and aim to measure the temperature (the latent variable), the measurements will be highly correlated because they originate from the same common cause (the reflective latent variable temperature); the correlations among thermometers are spurious and disappear once we condition on the latent variable. For depression, however, the assumption that symptom correlations are spurious is not only inconsistent with common sense (insomnia -> fatigue -> concentration problems) and residual dependencies among symptoms, but also contrasts with studies demonstrating that symptoms influence each other directly in complex dynamic systems Bringmann, Lemmens, Huibers, Borsboom, & Tuerlinckx, 2015;Fried, 2015).…”

Symptoms of posttraumatic stress disorder in a clinical sample of refugees: a network analysis

“…This is in contrast to the model of psychopathology used by current nosological systems such as DSM-5 (American Psychiatric Association, 2013) or ICD 10 (World Health Organization, 1992), in which symptoms are considered to be causally independent of each other and as being the result of an unobserved, latent entity (Hofmann, Curtiss, & McNally, 2016). This model has clinical and scientific importance, shifting the focus from finding the underlying cause of a defined psychopathological syndrome to the investigation of the symptoms’ interdependent relationships (Fried, 2015). …”

Vad är suicidalitet? Psykiaterkåren måste ena sig

“…Först på 1990-talet observerades ångestens avgörande betydelse för suicidhandlingar (Riskind 2000). Sannolikt är också den bild som DSM-systemet ger av depression betydligt förenklad (Fried 2015). Det är bl.a.…”