The Traditional Diagnostic Interview (TDI) is the basic technique clinicians use to make their initial psychiatric assessment. TDI consists of broad areas (chief complaint, history of present illness, past psychiatric history, family and personal history, mental status, diagnosis and treatment plan), with specific items in each area.
In 1996 I compared medical records from 10 different hospitals and clinics (including four university hospitals) and found that TDI is standardized in format-all hospitals used printed protocols for recording TDI. I also discovered that TDI is not standardized for content, the protocols differed widely from each other. So, too, many studies have shown that TDI often leads to inaccurate diagnoses.
The inaccurate diagnoses arrived at with use of the TDI have three main causes:
1. Incomplete data base: Lipton and Simon found that 80% of medical charts do not contain enough information to justify the stated diagnosis.
2. Incorrect/incomplete recording of data: May and Miller found that the longer you wait to write down your data, the more quantity and accuracy you lose-up to 50% in the first hour, 75% in the first eight hours.
3. Incorrect application and recall of DSM criteria. Skodol and colleagues found that 75% of incorrect diagnoses result from incorrect application of DSM criteria. Robinson and others found that 13% to 48% of the criteria for major depression were misidentified by a university-affiliated faculty. The written exams I give psychiatric residents find that they recall only about 50% of criteria for schizophrenia. They remember most symptoms but forget criteria about social/occupational dysfunction, duration of illness and other diagnostic exclusions. The most widely used statistical measure of diagnostic accuracy is interrater reliability.
Researchers regularly find that TDI has very low reliability. My own studies, in reports to the Los Angeles County Department of Mental Health (1995) and the corresponding Department of Mental Health Services (1997), agree: Using global diagnoses (defined by the first three digits of DSM-IV code, so that 295=all schizophrenia, 296=all mood disorders, 304=all drug dependence, etc.), we studied 50 patients who were diagnosed first in the emergency room and then on the inpatient service and found kappas of 0.01 for schizophrenia and 0.22 for mood disorders. For 100 outpatients who were diagnosed in 15 different clinics, kappas were 0.03 for schizophrenia and 0.16 for mood disorders for each pair of diagnosticians in sequence. When the statistical measure kappa is below 0.40, it indicates poor interrater reliability and inaccurate diagnoses.
The problem of TDI's diagnostic accuracy, as measured by interrater reliability, is almost totally ignored by clinical and academic psychiatry.
1. The two largest textbooks (Hales and colleagues; Kaplan and Sadock) have references about diagnostic reliability concerning methodology, epidemiology and specific areas of psychopathology, but none about reliability of TDI in real-time clinical practice.
2. The American Psychiatric Association bibliography of psychiatry, Core Readings in Psychiatry (Sacks and colleagues) contains 11 references dated 1961 to 1987 on diagnostic reliability, all of them about theory or statistics, none about real-time clinical practice using TDI.
3. A Medline search on interrater reliability for diagnosis (1990 to 1996) found 111 references. Most focused on a specific area of diagnosis (e.g., negative symptoms, bizarre versus nonbizarre delusions, schizophreniform disorder). Only two were about the real-time use of TDI as a global process.
Whenever research (including clinical trials) requires diagnostic reliability, investigators supplement or replace TDI with structured interviews or rating scales. But clinicians continue to use TDI alone, in spite of its proven limitations. Seeking to provide an improved assessment tool, I am now developing the Computer-Assisted Diagnostic Interview (CADI).