I am here as a committee member of the WorldHealth Organization Composite InternationalDiagnostic Interview (CIDI) Advisory Committee.The CIDI is the most widely used epidemiologicalscreening tool and has been used in some 20 inter-national surveys. It will be used over the next twoyears in ‘World Mental Health 2000’, a set of 10 dif-ferent country surveys all of the order of 5000–15 000respondents. By the end of the year 2000 it will havebeen administered to more than 400 000 adults inmany different countries and languages. The focus ofinterest is in the more common disorders such asanxiety, depression and substance use disorders andpeople are not quite as interested in the low preva-lence disorders like schizophrenia. In populationsurveys, it is very expensive to pick up enoughpeople with psychosis to make understandable deci-sions about what the data is telling you. For thisreason when we did our national mental healthsurvey in Australia two years ago, Assen Jablenskyheaded what was called the Low PrevalenceDisorders Survey [1] because it was realised that the

national survey of 10 000 people would only returnapproximately 40 or 50 people who might haveschizophrenia.

At another level there is a conceptual problem. TheCIDI was designed to be administered by lay inter-viewers [2]. Professional interviewers ask all thequestions listed on the paper but, as they have noclinical training to make judgements about what ispsychosis or whether the response is reasonable orunreasonable, they are unable to judge the presenceof psychosis. It may well be that something like theCIDI just cannot get near the diagnosis of psychosis.However, maybe it can, and that is what the presentpaper is about.

In the United States National Comorbidity Survey,the CIDI simply operationalised the diagnostic crit-eria in DSM-III-R. The questions that were asked inthe National Comorbidity Survey were: Do youbelieve people were spying on you?; plotting againstyou?; reading your mind?; reading your thoughts?;Could you actually hear what another person wasthinking?, etc. The University of Michigan (UM)CIDI does a little more than that, but not much. In theUnited States National Comorbidity Survey, 28% ofAmericans answered yes to one of these questions[3]. This demonstrated that asking people about psy-chotic phenomena is not very specific. Nevertheless,

Case ascertainment: the CompositeInternational Diagnostic Interview

Gavin Andrews

Objective: To outline the utility of the Composite International Diagnostic Interview(CIDI) in the diagnosis of psychosis.Method: Report current situation.Results: The CIDI was designed as a fully structured interview to be used by layinterviewers. It generates false positive diagnoses in community surveys and falsenegative diagnoses in psychiatric settings. A new psychosis module has been developed to reduce these problems.Conclusions: The diagnosis of psychosis by fully structured diagnostic interviewsis difficult.Key words: Composite International Diagnostic Interview, diagnostic interview.

Australian and New Zealand Journal of Psychiatry 2000; 34 (Suppl.):S161–S163

Gavin Andrews, Professor, School of Psychiatry

University of New South Wales, St Vincent’s Hospital, 299 ForbesStreet, Darlinghurst, New South Wales 2010, Australia. Email: gavina@crufad.unsw.edu.au

1.3% met criteria for narrowly defined psychoticillness and 2.2% for what was later called nonaffec-tive psychosis. The people with nonaffective psy-chosis were then telephoned and interviewed indepth. The detailed history of their illness and theirsymptoms was reviewed by Kendler, who has had alot of experience in the community determination ofpsychiatric illness. Kendler et al. reported that about50 of these people met strict criteria for nonaffectivepsychosis [4]. Hence, in the community, using ques-tions that address the diagnostic criteria and thathave face validity, the CIDI generates a number offalse positives.

To see if this false positive problem was general,Cooper and colleagues examined a clinical sampleusing clinician check lists with two clinicians anddemonstrated that there was a good relationshipbetween those clinicians’ check lists [5]. They werereliable and valid. The clinician check lists wereagain just an operationalisation of the diagnostic criteria (now DSM-IV). When the CIDI was com-pared with the check lists, the opposite effect washappening [5]. The CIDI was identifying positivesymptoms and missing the negative symptoms and,therefore, in a clinical sample, the problem was falsenegatives, or underestimates of the prevalence of psychosis.

How do you solve the problem of an instrumentthat in one environment produces false positives, yetin another environment produces false negatives?The CIDI used to ask people whether they have asymptom described in the diagnostic criteria and alsoask the interviewer (who was trained as an inter-viewer but not in mental health) whether theybelieved that this response was plausible. If the inter-viewer felt that the response was not plausible thenthat was scored as a positive symptom. The CIDI wastherefore modified to be more focused on the plausi-bility of the response. For example, the questions arenow phrased: Have you believed that people werespying on you?; How did you know these peoplewere spying on you?; Who was spying on you?; Wasit a lot of people, a few people or only one?; Was itsomeone you knew or a stranger?; What did theyhope to find out?; and What were they trying to do?Therefore, instead of a simple scoring of the criteriaif the interviewer decides, ‘yes, it is implausible’, amuch more subtle scoring of the ‘yes’, ‘no’ and‘uncertain’ codes is used before a symptom wasapproved as meeting the criteria for a diagnosis.

Section P of the original CIDI, which focused on allthe negative symptoms of schizophrenia, was then

examined. An example of one of the problems with theoriginal CIDI was that it questioned lay interviewersabout whether there were neologisms present, andcryptically defined this as ‘the use of made up ormeaningless words’. This contributed to problems ofreliability. It is not surprising that numerous false negatives were observed in a clinical sample wherethe negative symptoms in people who had the dis-order for a long time are important. Therefore, wehave written a new version of Section P in which eachsign is now fully described so that lay interviewerscan understand what they are being asked to rate. Themodified version of the CIDI has defined everythingin detail and the interviewers are trained to understandthe meaning of these terms. There is now evidencethat the interviewers are able to reliably make thesejudgements. We have compared a number of people ina clinical setting using the revised CIDI and theSchedule for Clinical Assessment in Neuropsychiatry.The revised CIDI is an improvement.

In the National Survey of Mental Health Well-being, there were actually a number of questionsdesigned to act as psychosis screeners; some from theUnited Kingdom psychosis screening questionnaireand others developed by Jablensky [1]. Each of themain questions asks about a putative psychotic experience and then checks that it is not an ‘X-File’phenomena. It questions whether the experiencecame about in a way that many people would findhard to believe; in other words, is it unusual orstrange? For example, question 2 asks: ‘In the past 12months have you had the feeling that people were toointerested in you?’. Question 2a asks whether ‘thingswere arranged to have a special meaning or even thatharm might come to you?’. Question 3: ‘Do you haveany special powers that most lack?’. It then does theinverse and question 3a asks: ‘Do you belong to agroup of people who also have these powers?’, toavoid falsely identifying, for example, a religiousgroup. A further question (G4) is, of course, the onewe all believe is the only real way to diagnose thedisorder: ‘Has a doctor ever told you that you mayhave schizophrenia?’. We developed a scorer for thisand the scores correlated with the CIDI. We nowhave to go back and rework our data against the original check lists which, after all, are a type of reliability standard. At the moment, in the survey,when you see people commenting about nonaffectivepsychosis, it means that people said ‘yes’ to G1A,G2A and said ‘no’ to G3A. Two or more of those getyou into the category known as a possible nonaffec-tive psychosis. The question about whether a doctor

COMPOSITE INTERNATIONAL DIAGNOSTIC INTERVIEWS162

has ever told you that you may have schizophreniadid not turn out to be a useful addition to the otherthree questions.

References

1. Andrews G, Hall W, Teesson M, Henderson S. The mentalhealth of Australians. Canberra: Mental Health Branch,Department of Health and Aged Care, 1999.

2. Andrews G, Peters L. Psychometric properties of the CIDI.Social Psychiatry and Psychiatric Epidemiology1998;33:80–88.

3. Kessler RC, McGonagle KA, Zhao S et al. Lifetime and 12-month prevalence of DSM-III-R psychiatric disorders inthe United States. Archives of General Psychiatry1994;51:8–19.

4. Kendler KS, Gallagher TJ, Abelson JM, Kessler RC.Lifetime prevalence, demographic risk factors anddiagnostic validity of non-affective psychosis as assessed in a US community sample. Archives of GeneralPsychiatry1996; 53:1022–1031.

5. Cooper L, Peters L, Andrews G. Validity of the CompositeInternational Diagnostic Interview (CIDI) psychosis module in a psychiatric setting. Journal of PsychiatricResearch1998; 32:361–368.

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