Understanding the International Dissociative Identity Disorder Questionnaire (IDIDQ) in 5 minutes
Andy H.W. Fung, PhD, RSW
Research Assistant Professor
School of Nursing, The Hong Kong Polytechnic University
andyhwfung@gmail.com / andy.hw.fung@polyu.edu.hk
What is the IDIDQ?
The IDIDQ is a 15-item self-report screening measure designed to measure (probable) dissociative identity disorder (DID) and partial DID as defined in ICD-11.
The IDIDQ was co-developed by three experts in the field of dissociation, including Hong Wang Fung, Vedat Şar (an official advisor to the DSM-5 Task Force of the American Psychiatric Association), and Colin A. Ross (the developer of one of the two existing diagnostic interviews for DID).
The IDIDQ was structurally similar to the International Trauma Questionnaire (ITQ) the International Adjustment Disorder Questionnaire (IADQ).
It assesses the three factors of DID, as proposed in ICD-11, including amnesia, dissociative identities, and switching.
It also assesses functional impairments and checks three specific exclusion criteria.
Why is it important?
The ICD-11 has updated the diagnostic requirements for DID and created partial DID as a new diagnosis. However, existing dissociation measures do not directly measure ICD-11 DID and partial DID. The validity of DID and partial DID as defined in ICD-11 requires more empirical investigation (Loewenstein et al., 2024).
Similar to the ITQ and the IADQ (Cloitre et al., 2018; Shevlin et al., 2020), the IDIDQ is short and easy to use. It also includes a simple diagnostic algorithm which maximizes clinical and research utility. Practitioners and researchers from around the world can use the IDIDQ to measure ICD-11 DID and partial DID, so that we can continue to enrich the empirical literature on complex dissociative disorders across cultures.
Why is it possible to use the IDIDQ to screen for DID and partial DID?
Previous studies showed that even self-report measures can detect complex dissociative disorders with good reliability and validity and have acceptable agreement with structural diagnostic interviews.
Most, although not all, patients with DID are aware of the presence of other dissociated self-states.
Other psychiatric conditions, such as ICD-11 complex PTSD, can also be reliably and validly measured using self-report measures.
How was the IDIDQ validated?
We pilot tested the IDIDQ in two convenience samples of mental health service users (118 Chinese speakers and 115 English speakers). We found that ICD-11 DID can be reliably and validly measured across cultures and languages using the IDIDQ. The IDIDQ had good to excellent internal consistency (α = .861 to .892) and test-retest reliability (ICC = .682 to .854, p < .001) in two convenience samples of mental health service users. The 3-factor structure of DID (i.e., amnesia, dissociative identities, and switching), as proposed in ICD-11, was supported by our cross-cultural data, with configural, metric and scalar invariance established across the Chinese- and English-speaking samples. The IDIDQ reliably detected probable ICD-11 DID and partial DID (κ = .517 to .781, p < .001) during a one-week test-retest period. The IDIDQ subscales were strongly correlated with the respective MDI subscales and the DES-T scores. The IDIDQ results had moderate to substantial agreement with the MDI Identity Dissociation subscale and the DES-T in both samples (κ = .514 to .741, p < .001). We have also conducted psychometric evaluation in other unpublished studies.
How can the IDIDQ be used?
The IDIDQ was designed to be an easy-to-use tool that can facilitate screening and cross-cultural research.
Its reliability, convergent validity, and factorial validity have been confirmed, but the diagnostic validity, including sensitivity and specificity, requires further research.
It is a useful screening measure, but it cannot replace diagnostic interviews. It has its strengths and limitations.
How to get a copy of the IDIDQ?
Currently, the IDIDQ is available in English and Chinese. Researchers and service providers who are interested in the IDIDQ can contact the developer via email: andyhwfung@gmail.com / andy.hw.fung@polyu.edu.hk
Researchers who want to translate the IDIDQ into other languages are welcome to contact us too.
Reference
Fung, H. W.*, Chau, A. K. C., Ross, C. A., Şar, V., Derin, G., Akiş, A. D., Chiu, H. T. S., Zatopek, A., & Ho, G. W. K. (2025). Measuring ICD-11 dissociative identity disorder: Cross-cultural validation of the International Dissociative Identity Disorder Questionnaire. Asian Journal of Psychiatry. https://doi.org/10.1016/j.ajp.2025.104685