Per Bech: Clinical Psychometrics

Per Bech’s reply to Aitor Castillo’s commentary

As a clinical psychopharmacologist Aitor Castillo has in contrast to many of the other reviewers of my book on clinical psychometrics especially focused on the Pharmacopsychometric Triangle. This part of the book was the most central element in my book and I am therefore very pleased to see how Aitor Castillo has metabolized the triangle.

In psychometric terms we use “responsiveness” of a rating scale or questionnaire to indicate its ability to measure a relevant change when comparing active medicine against placebo in randomized, controlled clinical trials. Clinically we use “response” of a psychopharmacological drug to indicate the symptom reduction in the condition being treated from baseline to endpoint when compared to placebo in such a randomized, controlled clinical trial.

To express “responsiveness” or “response” we use the new statistics of effect size as emphasized by Aitor Castillo. The statistical significance as expressed by a p value cannot as stated by Cumming (1) provide the answer to a “how much?”, which is the question asked for when measuring a clinical significant “responsiveness” by a rating scale or a questionnaire. Therefore, when using the Pharmacopsychometric Triangle we have to use effect size statistics when comparing (A) the amount of reduction of clinical symptoms, with (B) the amount of undesired side effects induced by the psychopharmacological drug, and (C) calculating the benefit of the treatment in the patient’s self-reported measure of improved well-being.

With reference to the Pharmacopsychometric Triangle it is, therefore, essential that rating scales measuring the desired clinical symptom reduction do not contain symptoms covering the undesired side-effects of psychopharmacological drugs as correctly emphasized by Aitor Castillo who refers to dose-response relation trials, for example, of antidepressive medicine.

My recent book on Measurement-based care (2) has actually the Pharmacopsychometric Triangle as its platform. It is an attempt to apply in the practical, routine treatment plan with psychopharmacological medication the short rating scales or questionnaires whish have been found valid in the randomized, placebo-controlled clinical trials taking the Pharmacopsychometric Triangle into account.

References:
1)  Cumming G. Understanding the new statistics: Effect sizes, confidance intervals, and
      metaanalysis. London: Routledge; 2012.

2)  Bech P. Measurement-based care in mental disorders. Springer Briefs in Psychology.
      Springer Verlag, New York 2016.

February 9, 2017