Item Response Modeling of Presence-Severity Items: Application to Measurement of Patient-Reported Outcomes

The Presence-Severity (P-S) format refers to a compound item structure in which a question is first asked to check the presence of the particular event in question. If the respondent provides an affirmative answer, a follow-up is administered, often about the frequency, density, severity, or impact of the event. Despite the popularity of the P-S format in areas such as patient reported outcomes, little attention has been paid to their psychometric analysis, which is necessary for making key design decisions about a scale. In this study, an item response theory-based framework is proposed to perform item analysis involving P-S data, which improves psychometric analysis for (a) scoring response categories, (b) calibrating items, (c) calculating reliability or internal consistency, and (d) selecting and revising items. A real-data example involving the Memorial Symptom Assessment Scale-Short Form, which is used as symptom distress measure for terminally ill cancer patients, demonstrates how the new framework can be used to address various psychometric issues in practice.