“What Is Actually Being Measured?”: Causality and Underlying Scientific Thinking Process in the Assessment of Depression

“What Is Actually Being Measured?”: Causality and Underlying Scientific Thinking Process in the Assessment of Depression Greta Kaluzeviciute-Moreton, PhD (bio) Depression is a complex mental health phenomenon due to its multifaceted nature. For one, depression is thought to have a significant genetic component, with studies suggesting that heritability is a significant factor in the development of the disorder (Sullivan, Neale, Kendler, 2000). In clinical psychology, environmental factors such as childhood trauma, chronic stress, social isolation and negative life events (e.g., the loss of a loved one) have been documented as significant risk factors for the development of depression or as trigger events for depressive episodes (Fu & Parahoo, 2009; Kendler, Kuhn, & Prescott, 2004; Neitzke, 2016). Despite this, causal theories of mental health conditions are often tricky and/or scarcely reflected in both diagnostic and rating scales. For instance, the Diagnostic and Statistical Manual of Mental Disorders classifies mental health disorders primarily based on observable symptoms and behaviors, rather than on the underlying psychological and neurobiological processes that may contribute to these symptoms (Kendler, 2006). Similarly, rating scales for depression are typically designed to assess the severity of symptoms, rather than their underlying causes, that is, most rating scales are used as screening tools to identify individuals who may require further evaluation and treatment. Some rating scales may include items related to causal factors, such as the Beck Depression Inventory-II (BDI-II) includes an item that asks about “loss of interest in sex,” which could be related to either biological or psychological factors. Several rating scales include items assessing risk factors for depression, such as family history of depression or personal history of trauma. This may be indicative of both genetic and environmental risk factors, such as the Patient Health [End Page 255] Questionnaire-9, includes an item that asks about family history of depression. However, while risk and causal factors are related, they are distinct in the assessment of depression. Risk factors refer to factors that increase the likelihood of developing depression, while causal factors refer to factors that directly contribute to the development of the condition. The presence of a risk factor does not necessarily mean that an individual will develop depression (Peterson & Seligman, 1984). However, the two are frequently blurred and equated in psychotherapy research (Westen & Bradley, 2005). As such, the historical issues of rating and diagnostic scales, aptly depicted by the Le Moigne (2023) as full of “composite, if not contradictory, heritage, weaving together the classificatory and discontinuous tradition of psychiatry, on the one hand, and the psychometric and continuous tradition of psychology, on the other” (p. XX), suffer from an epistemological oversight when it comes to the assessment of causal factors in complex mental health conditions, such as depression. In turn, this contributes to a wider psychometric issue: what is actually being measured? Le Moigne’s detailed overview predominantly focuses on “superficial” symptomatology of depression (which contributed to two distinct forms of evaluation: hetero- and self-evaluation), and its subsequent impact on the classification and taxonomy of depression throughout history. However, the overarching conceptualization of depression (including a more detailed consideration of causal factors and their assessment) and the usefulness of rating scales in applied research (such as psychotherapy) remain in the background. The question of “what is actually being measured” is obviously not new in psychometrics. However, it is important to continuously revisit this issue, given that rating scales (such as the BDI) are considered to be universally applicable “evidence-based” tools (Rogers, Adler, Bungay, & Wilson, 2005) as well as a common and well-accepted form of scientific thinking in psychotherapy research (Kaluzeviciute & Willemsen, 2020). From an epistemological point of view, a scientific thinking style entails not only cognitive operations common to methodology, but also practices of generating, sharing, assimilating and transforming knowledge (Hacking, 2012). Therefore, it is important to acknowledge that any scientific tool, including rating scales, encompasses not just what but also how researchers find out about their studied phenomena (i.e., a scientific thinking style conveys a performative quality) (Kaluzeviciute & Willemsen, 2020). As identified by Le Moigne (2023), taxonomy leads toward a category-based logic in that it considers the examined phenomenon to be shared by only a...