Can Short-Form Questionnaires Substitute Full-Scale Questionnaires to Evaluate Psychopathology?

We all know the importance of measurement. It is important to get the measurement right! However, all too many well-intentioned researchers and clinicians get it wrong.

In a new study published today, Per Carlbring and I discuss how brief versions of the PHQ and GAD can be used to effectively monitor in-treatment fluctuations in psychopathological symptoms.

BRIEF VS EXTENSIVE MEASUREMENTS

Extensive measurements like the Beck’s Depression Inventory can provide a comprehensive snapshot of the current depressive symptom presentation. However, aside from licensing issues, it is quite burdensome in administration. The PHQ-9 includes all nine symptom criteria for major depression and thus should theoretically be informative for quantifying symptom severity. However, it is not self-evident that frequent administrations of the PHQ-9 provide an appropriate representation of depressive symptomatology.

Furthermore, cutoff points for the PHQ-9 can be misleading; there are no inherent guidelines about how one should interpret total scores with the DSM diagnosis criteria in mind. For instance, for a diagnosis of depression, you need to have either a depressed mood or anhedonia, criteria which are reflected in the first two items of the PHQ-9. However, consider a client who has a high total score on the PHQ-9 but does not endorse the first two items, thereby negating a diagnosis while the recommended cutoff point erroneously leads us to conclude that the client meets criteria for major depression.

Brief measures on the other hand are easy to administer and arguably easier to interpret. Consider the PHQ-2, which only includes items that are necessary, although not sufficient, to diagnose depression. Due to its brevity and relevant items for diagnosis, a client who endorses these first two items is more likely to meet diagnostic criteria for major depression.

Let’s call out the elephant in the room: Two-item scales are self-evidently not going to provide an equally comprehensive snapshot of the symptom presentation of each individual. However, their total scores do an equally good job in discriminating clients who are likely to meet diagnostic criteria as their full-scale counterparts.

Our recent study provides support for the notion that argue that brief short-form versions are and ought to be prioritized over their extensive full-scale counterparts to monitor in-treatment fluctuations in treatment outcomes. This is due to the isomorphic discriminative capability between the short-form and full-scale versions of the PHQ and GAD.

Furthermore, recent systematic reviews suggest that most anxiety and depressive symptom severity scales don’t fully capture the entire breadth of the idiosyncrasies of these disorders anyway, and therefore we are left with the question of why we should burden clients with extensive measures to begin with if similar outcomes can be obtained using short-form measurements.

SUMMARY

Brief measures of depression and anxiety are equally good at discriminating between clients who meet criteria for major depression and anxiety as their full-scale counterparts. This is true during pre-treatment screening, at post-assessment, and during the treatment itself.

However, we caution against using these brief measures for other purposes than to monitor in-treatment symptoms since they do not provide a holistic image of the symptom presentation – for instance, if the PHQ-2 were used during pre-treatment screening, we would not have access to information about suicidality. Instead, we recommend the use of brief measures like the PHQ-2 and GAD-2 to be constrained to monitoring in-treatment symptoms.

Due to their extreme brevity, these measures can be administered with much greater frequency than their full-scale counterparts and future studies should aim to incorporate them in ecological momentary assessment protocols.

You can read more about these results here!

Hlynsson, J. I., & Carlbring, P. (2024). Diagnostic accuracy and clinical utility of the PHQ-2 and GAD-2: A comparison with long-format measures for depression and anxiety. Frontiers in Psychology, 15. https://doi.org/10.3389/fpsyg.2024.1259997

The post Results From a New Study on the PHQ-2 and GAD-2 first appeared on Jón Ingi Hlynsson.