Reply to the Letter to the Editor: “Is A Single-Item Measure of Self-Rated Mental Health Useful from a Clinimetric Perspective?”

Abstract

Similar considerations apply to observer-rated scales and the clinical interpretation of diagnostic criteria [4]. All components of diagnostic criteria are weighed equally, unlike in clinical medicine, where major and minor symptoms are often differentiated. The hidden conceptual model is psychometric: severity is determined by the number of symptoms, not by their intensity or quality, to the same extent that a score in a depression self-rating scale depends on the number of symptoms that are scored as positive [4]. Not surprisingly, the sensitivity of global methods of assessment is acknowledged in drug trials, where they often yield the most sensitive discrimination between drug and placebo effects [5]. In psychometrics, a high correlation is often regarded as evidence that the two scales measure the same factor. However, a high correlation does not indicate similar sensitivity: a common content of two scales may insure a high positive correlation between them, but the items they do not share may be important in determining their sensitivity [4]. In clinimetrics, homogeneity of components is not requested, and items may be weighed in different ways: what matters is the capacity of an index to discriminate between different groups of subjects and to reflect changes in experimental settings such as drug trials [4]. Single-item clinimetric indices may display higher sensitivity than complex and time-consuming questionnaires in certain clinical situations. Casu and Gremigni [1] have provided interesting data on the neglected issue of single-item self-rated indices. A comment worth adding is the fact that, according to the psychometric model, severity results from the sum of the single items that are part of a scale. All items are weighed equally. However, in self-rating instruments, not all items carry the same weight for the patient (certain symptoms may be more important or troublesome than others). The one item index does not present such disadvantages since it covers a specific level of symptom severity [2]. In psychometric rating scales, many items are redundant as they measure parallel formulations of the same symptom. Further, in the psychometric model, the severity of the clinical condition is determined by the sum of items, and the relationships among numbers are represented by a simple additive effect, regardless of reciprocal interactions [3]. In expressing a self-evaluation, the subject formulates a global appraisal that goes beyond the simple sum of all items included in a rating scale. Clinicians use the single item to provide an initial global assessment, and the evaluation is often closer to the core symptoms of patients [2]. Received: January 30, 2019 Accepted after revision: February 6, 2019 Published online: April 1, 2019