Improving the Measurement of Functional Somatic Symptoms With Item Response Theory.

Angélica Acevedo-Mesa,Judith G M Rosmalen,Annelieke Roest,Rei Monden,Jorge Nunes Tendeiro

doi:10.1177/1073191120947153

Angélica Acevedo-Mesa, Judith G M Rosmalen + Show 3 more

Open Access

https://doi.org/10.1177/1073191120947153

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Abstract

More than 40 questionnaires have been developed to assess functional somatic symptoms (FSS), but there are several methodological issues regarding the measurement of FSS. We aimed to identify which items of the somatization subscale of the Symptom Checklist–90 (SCL-90) are more informative and discriminative between persons at different levels of severity of FSS. To this end, item response theory was applied to the somatization scale of the SCL-90, collected from a sample of 82,740 adult participants without somatic conditions in the Lifelines Cohort Study. Sensitivity analyses were performed with all the participants who completed the somatization scale. Both analyses showed that Items 11 “feeling weak physically” and 12 “heavy feelings in arms or legs” were the most discriminative and informative to measure severity levels of FSS, regardless of somatic conditions. Clinicians and researchers may pay extra attention to these symptoms to augment the assessment of FSS.

Highlights

A symptom is defined as a bodily sensation or mental experience subjectively perceived as a change from normal health (Rhodes & Watson, 1987)
This study aimed to identify which of the Symptom Checklist–90 (SCL-90) somatization scale items most accurately reflected varying levels of severity of functional somatic symptoms (FSS) and better discriminated between different levels of severity of FSS, in a sample of participants without somatic conditions
High levels of severity of FSS were necessary for a person to report the higher answer options on the items of the SCL-90 somatization scale, which was reflected in the high threshold parameters (β)

Summary

Introduction

A symptom is defined as a bodily sensation or mental experience subjectively perceived as a change from normal health (Rhodes & Watson, 1987). The cut-off scores used to classify patients by the severity of FSS vary among questionnaires and are based on the sum score of each questionnaire (Zijlema et al, 2013) This disguises the individuals’ severity of FSS since it ignores the specific types and frequencies of the symptoms reported individually. When applied to the construct of the severity of FSS, IRT models provide information about which items are more able to discriminate between persons with different levels of severity of FSS, as well as which items represent higher or lower severity of FSS based on their probability of being reported This is especially relevant for research on FSS due to the heterogeneity of symptoms and the difficulty to measure the severity of FSS.

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