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Friday, 28.04.2017

Per Bech: Clinical Psychometrics

Per Bech’s reply to Hector Warnes’ commentary

 

Hector Warnes has made a very accurate and comprehensive review of the contents of my book, much better than my own. I am very impressed by the background knowledge he shows concerning my heroes like Eysenck, Hamilton, Pichot and Overall. Of them, it was Pierre Pichot who really understood my use of the Rasch item response analysis, and who told me that I was the first to use a Rasch rating scale model. This aspect has also been captured by Hector Warnes who emphasizes that this model can only be applied when a clinical validity has been obtained for the scale.

I agree fully with Hector Warnes that I could have written more extensively about Feinstein’s concept of clinimetrics. In his 1987 monograph, Feinstein refers to the clinical term “improvement after treatment” as an example of a concept with clinimetric importance which no biological marker can measure.

I also see a clear limitation in my “rather pragmatic view” on very brief, easy-to-use rating scales. There are, as stated by Hector Warnes, many variables at play in outcome ratings of treatment. However, in this situation I would like to recall my meeting with John Overall at the annual NCDEU meeting in 1987.  He chaired a session on his Brief Psychiatric Rating Scale (BPRS) where I presented a 10-item BPRS schizophrenia subscale tested by the Rasch model. After the session, John Overall told me that a brief rating scale should not have more than 18 items and when I had selected the 10 items relevant for schizophrenia I still need some extra “contact-inducing” items to open the interview with the patient, as well as items to finish the interview.

Actually, in my comment on the Heinz Lehman biography by Barry Blackwell (2015) I mentioned that I have access to Lehman’s videotaped interviews with schizophrenic patients using the BPRS (Bech, 2016). These interviews last approximately 25 minutes.

 In the tapes, Heinz Lehman shows how to conduct a flexible, non-structured interview in which his “contact-inducing” items are about sleep and appetite, then comes the specific schizophrenia-relevant items and he finalizes the interview by asking about suicidal thoughts.

This is what Hector Warnes is so correctly looking for, i.e., even a short rating scale has to be conducted in an interview of at least 25 minutes.

When evaluating “improvement after treatment” we have to use rating scales referring to the underlying change over time on the latent dimension being measured, i.e., the antipsychotic effect on the BPRS subscale. This clinimetric issue was not included in the DSM-5 because David Kupfer was not successful in adopting the dimensional approach. I agree with Hector Warnes that such a breakthrough in the genetic field, as shown by Jordan Smoller, soon will help us identify the biological markers we need in clinical psychiatry. However, in the intervening time, we have to rely   much more on the dimensional approach inherent in the clinically valid rating scales.

 

References:

Bech P. Comment on Barry Blackwell’s Heinz Edgar Lehmann. Inhn.org; Biographies. February 4, 2016.

Blackwell B. Heinz Edgar Lehmann. Inhn.org; Biographies. November 5, 2015.

 

January 26, 2017