The movement to a descriptive, symptom-based diagnostic system that started with the DSM-III was in part a response to widespread concerns and criticisms regarding the reliability of psychiatric diagnoses. This fueled an emphasis on increasingly precise operationalization of diagnostic constructs and criteria, based on the assumption that this would produce successive improvements in reliability.

Clinician-administered structured diagnostic interviews were subsequently developed. For example, the Research Diagnostic Criteria were used to develop a Schedule for Affective Disorders and Schizophrenia¹, while the DSM-III criteria were incorporated into the Structured Clinical Interview for DSM (SCID)². In addition, the Diagnostic Interview Schedule³ was developed for use by non-clinician interviewers in epidemiological surveys of mental disorders. These instruments have been widely used in research on mental disorders.

Structured diagnostic interviews have subsequently been developed or adapted for successive revisions of the DSM and the ICD. The SCID, a semi-structured interview – meaning that the interviewer probes unclear responses and makes certain clinical judgments – has been updated with each edition of the DSM⁴. The briefer and fully structured Mini International Neuropsychiatric Interview (MINI)⁵ has also been widely employed. The Composite International Diagnostic Interview (CIDI)⁶ incorporated both DSM and ICD diagnostic requirements and was used in the National Comorbidity Survey and the World Mental Health Surveys. Similarly, the Schedules for Clinical Assessment in Neuropsychiatry (SCAN), based on the Present State Examination, assessed for both DSM and ICD requirements⁷. Structured diagnostic interviews for children have also been developed, as have a range of more focused interviews that cover specific conditions or diagnostic groupings.

Based on an extensive program of field testing, the reliability of the diagnostic guidance provided in the Clinical Descriptions and Diagnostic Requirements for ICD-11 Mental, Behavioural and Neurodevelopmental Disorders (CDDR)⁸ was found to be higher than that of other mental disorder classification systems, ranging from moderate to almost perfect according to the specific category. This finding was perhaps counterintuitive, insofar as the CDDR avoid highly prescriptive symptom counts and duration requirements, unless these are specifically supported scientifically, in order to facilitate clinical use.

These results, therefore, challenge the assumed relationship between operational precision and diagnostic reliability. They also suggest that the diagnoses based on the CDDR would be sufficiently reliable for certain types of research projects (e.g., studies focusing on diagnostic groups in health care settings). However, in other types of research, standardized diagnostic assessments are desirable to control clinician-level variability associated with different skill levels, interviewing styles, and clinical judgment. For example, in pharmacological trials that select participants based on certain diagnostic requirements, the ability to document specific symptom patterns reliably and reproducibly is often important. Epidemiological or other population-based surveys involving lay (i.e., not clinically trained) interviewers also require pre-scripted questions and strict decision rules, because they cannot rely on the interviewer's clinical knowledge to determine whether specific features are present.

Diagnostic interviews have therefore been a part of the work plan related to the CDDR nearly from the beginning. The relevant work has employed a rigorous development process and included international experts in the fields of nosology and diagnostic interviews. Work on the Structured Clinical Interview for ICD-11 (SCII-11) has been ongoing since 2014. This is a semi-structured diagnostic interview – designed to be administered by a trained clinician – that provides a standardized set of questions, each assessing a specific diagnostic requirement for the purpose of formulating a differential diagnosis. Though developed for research applications, the SCII-11 will also be useful for training purposes and in clinical settings.

Due to the CDDR's more clinically-oriented framing of diagnostic requirements, additional operationalization has been necessary in developing the SCII-11. Specifically, the SCII-11 substitutes more precise diagnostic thresholds for less prescriptive terms in the CDDR (e.g., at least three rather than “several” symptoms; at least three months rather than “persistent”). In addition, specific questions have been developed for elements of the CDDR that may manifest in a variety of different ways (e.g., “persistent delusions” in schizophrenia).

The World Health Organization (WHO) Flexible Interview for ICD-11 (FLII-11) is being developed as an open-access tool to support national epidemiological investigations and other population-based and clinical studies of mental disorders. It is a fully structured diagnostic interview that can be administered by trained lay interviewers and assesses mental disorders associated with the greatest global disease burden. It builds on the operationalization work completed for the SCII-11. Like the SCII-11, the FLII-11 is modular and customizable to assess a subset of disorders, and can evaluate current and lifetime diagnostic status. Available modules include psychotic, mood, anxiety, obsessive-compulsive and related, post-traumatic, eating, addictive behaviour, and substance use disorders, and attention deficit hyperactivity disorder. An adaptation for adolescents aged 13-17 has also been developed.

There has been a high level of interest in the FLII-11, due to the increasing global importance given to mental disorders, and the desire of WHO member states to use an open-access measure that is consistent with the current official global diagnostic system. The FLII-11 is being prepared for feasibility testing, including review by people with lived experience, as a part of an international collaboration that involves Brazil, China, India, Liberia, Mexico, South Africa, Sri Lanka, Tunisia and Uganda. This is occurring in tandem with its use in national mental health surveys in several of these countries.

The FLII-11 is being translated into multiple languages and employed in a broad range of settings around the globe. It is therefore critical that complex concepts be phrased in readily understandable and culturally appropriate ways. This has necessitated the development of a standardized cultural adaptation and translation process. The WHO aims to develop an online platform that will facilitate the collection, analysis and sharing of international data and become a resource for international mental health epidemiology.

Diagnostic interviews based on the ICD-11 CDDR promise to be useful for both clinicians and researchers. At the same time, several concerns should be borne in mind as this work proceeds. A first concern relates to the limitations of an approach to diagnostic assessment of mental disorders that relies primarily on direct self-report of their essential features. There are also concerns about areas in which interviewees may have an incentive to minimize or deny their symptoms (e.g., when they relate to illegal or highly stigmatized behaviours), or when an aspect of the presentation is poor or absent insight or a distorted view of their own behaviour and functioning. Validation of diagnostic interviews in these areas requires particular attention.

Another ongoing question is how best to validate an interview undertaken by an experienced clinician. Spitzer proposed using a “longitudinal expert all data (LEAD) standard”⁹, which is difficult and burdensome to do and still subject to clinician bias. New diagnostic measures are more commonly validated against other measures; for example, results of the lay-administered FLII-11 could be compared to those of the clinician-administered SCII-11, rather than against a measure not based on the ICD-11. The issue of false positives in epidemiological research remains a concern and must be evaluated, but may be ameliorated by training.

Establishing the cross-cultural feasibility and validity of structured diagnostic interviews for the ICD-11 will provide an important foundation for international mental health research.