Response to “Clinical Outcome Assessment Instruments in Schizophrenia: A Scoping Literature Review with a Focus on the Potential of Patient-reported Outcomes”

Dear Editor:

As co-author of the Epidemiological Study of Cognitive Impairment in Schizophrenia (EPICOG-SCH), also known as EPICOG-SCH brief battery, I wish to address an error in the article, “Clinical Outcome Assessment Instruments in Schizophrenia: A Scoping Literature Review with a Focus on the Potential of Patient-reported Outcomes.”¹ In Table 3, titled Schizophrenia-specific ClinRo/ObsRos (clinician-reported outcomes/observer-reported outcomes), specifically in the 11th row (Page 21, Table 3, CONT), the EPICOG-SCH battery is mentioned, but the description of the instrument is inaccurate in terms of the instrument type, the domain covered, and the interpretation. We are pleased that the instrument has been considered, and we would like to suggest the following addendums.

At the “Domain” column, the instrument is described as a measure of “symptomatic” domain, but it should labeled as “Cognition” instead. The EPICOG-SCH battery is a type of performance-based clinical outcome (PerfO) and consequently is composed of subtests that require the subject to perform specific tasks. The battery includes the subtests: WAIS- Letter-Number-Sequencing (LNS), WAIS-Digit-Symbol-Coding (DSC), WAIS-Logical-Memory Immediate Recall (LM), and Category Fluency Test (CFT) involving three categories (Animals, Fruits, Cities-Villages).

It is also relevant to draw attention to the title of Table 3, which should be “Schizophrenia-specific ClinRO/ObsRO/PerfOs” or the even more generic “Schizophrenia-specific Clinical Outcome Assessment Instruments” instead of the original title that only mentions ClinROs/ObsROs. Table 3 includes several types of instruments that would be better represented if the title were adjusted as suggested.

Furthermore, under the “Interpretation” column, the statement about how to interpret the results is not precise and can be misleading. Following the administration of the EPICOG-SCH battery, scalar values are obtained for five subtests (mean: 10, standard deviation [SD]: 3) and two global composites (Unitary Composite and Functional Composite) scaled to a mean of 100 (SD: 15); higher score equals better cognition. For the Functional Composite score, a higher score means better cognition and functionality in daily life. In this way, the EPICOG-SCH algorithm is easy to interpret because with the Functional Composite, there is provided the functionality associated with a patient’s cognitive level. Functional Composite is validated with a cutoff score of 96 or greater for fair functionality. The normative sample for the interpretation is the epidemiological study composed of 672 stable patients diagnosed with schizophrenia.

It is important to note this addendum to the original because EPICOG-SCH is a PerfO, which means it is an objective measure, and also because the “Interpretation” column mentioned the method used for the calculation of prevalence for cognitive impairment in the epidemiologic study as published by Zaragoza Domingo et al (2015).² However, the final validation and interpretation of the EPICOG-SCH battery were described and published elsewhere (Zaragoza Domingo et al [2017]).³ A more detailed description of the battery can be found at the instrument library from Mapi Trust Foundation.⁴

With regards,