Behavioural Brain Research 259 (2014) 9–15 Contents lists available at ScienceDirect Behavioural Brain Research j ourna l h om epage: www.elsevier.com/locate/bbr Research report Validity, reliability and prevalence of four ‘clinical content’ subtypes of depression Christopher F. Sharpley a,∗ , Vicki Bitsika b a Brain-Behaviour Research Group, University of New England, Armidale, NSW 2351, Australia b Brain-Behaviour Research Group, Bond University, Gold Coast, QLD 4229, Australia h i g h l i g h t s • Global Depression may be subdivided into clinical content subtypes. • Validity of those subtypes is based upon symptomatology. • Reliability is demonstrated for each subtype via data drawn from three populations. • Prevalence indicates individual differences in subtype profiles. • Individualised treatment planning requires consideration of these subtypes. a r t i c l e i n f o Article history: Received 22 September 2013 Received in revised form 13 October 2013 Accepted 18 October 2013 Available online 27 October 2013 Keywords: Depression Diagnosis Assessment Clinical Validity Reliability a b s t r a c t Although depression is often diagnosed via reference to a list of nine criteria which may be used to form a unitary diagnosis, there is significant variation in the content of those nine criteria to justify consider- ation of four ‘clinical content’ subtypes of depression based upon differences in symptomatology. Each of those four subtypes has previously been described for their different causes, underlying neurobiologi- cal pathways, and treatment requirements. This paper reports on the validity, reliability and prevalence of those four subtypes of depression across three samples of participants. Validity is demonstrated and satisfactory reliability values are reported for each subtype, plus significant correlations between items used to measure each subtype, arguing for the individual homogeneity of each of these four subtypes. Prevalence data indicated that there were significant subtype differences at the sample and individual level, challenging the usage of a single global depression score. These results argue for further consider- ation of these subtypes when researching depression and in planning individualised treatment regimes. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Clinical and subsyndromal depression adversely affect physical health, relationships and cognitive performance [1–3], and pro- duce the greatest decrement in personal health [4] and the highest cost of care [5]. As a result, depression has been described as the major contributor to the total disease burden [6] and continues to be the second most common contributor to years lived with dis- ability [7]. Some data suggest that depression poses a similar risk as does smoking for mortality from all causes, even when related health factors such as blood pressure, alcohol intake, cholesterol and social status are taken into account [8]. Treatment of depression assumes accurate identification of depressed persons, the severity of their depression, and the ways ∗ Corresponding author. Tel.: +61 7 5536 8386; fax: +61 7 5599 4778. E-mail address: csharpley@onthenet.com.au (C.F. Sharpley). in which the depression they experience influences their physical and mental health. The ‘gold standards’ in assessment of depressive symptomatology are the ICD and DSM classification systems for Major Depressive Disorder (MDD), which provide diagnostic criteria that include cognitive, emotional and physiological symptoms and which may be used within structured interviews or applied by self- report scales to assess the presence and severity of depression. The diagnostic criteria for MDD are shown in column 1 of Table 1. 1.1. Different types of depression Despite the most common outcome of assessment for MDD being a unitary diagnosis (i.e., either MDD is present or not), that process ignores the fact that there may be different varieties or “subtypes” of depression. For example, Halbreich [9] suggested that clinical assessments for depression might allow for the presence of multiple symptom groups of the diagnostic criteria for MDD, and Baumeister and Parker [10] found 15 such depression subtypes that 0166-4328/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bbr.2013.10.032