Potential Benefits

Some of the more commonly reported benefits include; improving communication, providing descriptive and predictive information (not to be confused with explanatory information), and forming the basis of theory (Blashfield & Draguns, 1976; Krueger et al., 2023)

These ‘benefits’ mirror that of the reported functions of contemporary classification systems. The WHO (ICD) and APA (DSM) have noted their position on their respective systems functions, which can be viewed here and here, respectively. In sum, both parties reference; (1) communication/common language, (2) informing diagnostic decisions and (3) collection and accessibility to descriptive information.

Theory to Practice Gap

Unfortunately, these reported benefits have seemingly failed to make their way to clinical/practical settings.

Surveying various mental health clinicians (n = 1,764) on how they practically use existing systems displays they often turn to ‘additional texts’ when in need of resources that act in such a functional manner (First et al., 2018). When participants were asked to prioritise the functions of such a system, the facilitation of communication and providing information inform treatment decisions were most consistently noted as the top priorities, although up to seven independent functions were noted (First et al., 2018).

Clearly, classifying psychopathology in an effective manner which allows the realisation of the reported benefits, is laden with challenges.

Luckily, there is no shortage of attempts at developing a replacement system that effectively addresses the limitations of the current systems. The RDoC Framework, HiTOP, Network analysis models (Denny Borsboom et al., 2013; Insel et al., 2010; Kotov et al., 2017), have developed/are developing novel ways of addressing theoretical and practical challenges.

A particular challenge, however, is that the precise role of a psychological taxonomy still remains unclear.

This lack of clarity is likely due to multiple factors, including the growing number of parties who are influenced by such a system.

Regardless, attempts to serve so many functions with a single taxonomy will likely negatively impact its realised utility.

The Problem with Multiple Functions

Developing a taxonomy requires ‘taxonomic resources’ (t). That is, (1) time for development (2) valid theory to draw from (3) researchers and clinicians to practically build the taxonomy (4) applicable funding, and (5) methodological sound research studies to clarify theoretical ambiguity, time in which to be developed.

Developing a taxonomy also requires the goals/functions (f) of the taxonomy to be known.

Once both t and f are known; t need to be distribution and allocated to each f, which may have a particular ‘resource threshold’ (rt) to be appropriately met.

If rt > t, the function won’t be effectively realised. Increased functions diminish resources available to each.

Each function may have particular resource ‘thresholds’ for that function to be appropriately met.

Thus, by assigning a taxonomy so many functions, you risk none of them meeting their threshold, either in a vacuum or via resources being competed over by other functions.

Simply, t > (f + ft).

An example with only two functions

Being conservative, it could be argued that substantial variance in the existing functions could be explained with two functions:

1. Improve Communication
2. Provide Clinical Utility (that is, assisting in diagnosing, predicting prognoses, etc)

Let's consider how integrating both functions into a system may work:

Prioritising Clinical Utility

It may make sense to build the classification system on theories found in complex network analysis models (Denny Borsboom et al., 2013).

These models can be effective at predicting behaviour, explaining comorbidity (bridge symptoms), and informing treatment by identifying key mechanisms of pathology (central nodes).

However, complex networks can be difficult to describe semantically with natural language, the clue is in the name (complex). This issue of semantic accessibility is compounded when the system is used in the context of individuals not familiar with such models.

So we need to turn to communication. Perhaps the system can classify disorders as latent variables, and symptoms or ‘diagnostic criteria’ can refer to more general constructs , avoiding any technical jargon. These constructs will be easily communicated between parties. However, as language becomes more generalised, clinical precision and accuracy of comprehension may lessen.

Simply, if clinical utility is prioritised, then the semantic accessibility of a taxonomy can be reduced. Similarly, increasing the efficacy of communication can reduce clinical utility.

What to do? Restrict or Prioritise The Functions

How do taxonomies prioritise functions, and subsequently, how do they serve the interests of various invested parties?

Attempting to evenly serve each stakeholder and each proposed domain will likely lead to a cumbersome, complicated taxonomy, which is inevitably disregarded and replaced with ‘clinical judgment’ until a diagnostic code is needed for paperwork.

This problem is only exacerbated by psychology’s current theoretical limitations. Unlike chemistry and its periodic table, psychology does not yet have a sound theoretical foundation to lean on as heavily as other fields do.

Given psychology youth, we may have to be modest with our expectations of a practical and accurate taxonomy.

Reduce the functions of a single classification system and delegate the additional functions to other parties/groups. Alternatively, prioritise functions in a ranked order, making it clear what a systems primary function is.

Implications

Reducing and delegating functions, or at least explicitly prioritising functions may.

• Better orientate clinicians and researchers on when to refer to the classification system, and when to refer to alternative sources.
• Delegate remaining functions or purposes to alternative texts/sources. For instance, mapping diagnoses onto treatment may be the role of X instead of a classification system.
• Clarify theoretical assumptions, even if only in a pragmatic manner. Doing so may encourage collaboration amongst researchers, to work on constructing theory which serves as a genuine theoretical foundation. In contrast to teams of researchers, who are well-funded funded, well-trained, but each working on their own individual theories and frameworks.