Improved Items for Estimating SF-36 Profile and Summary Component Scores: Construction and Validation of an 8-item QOL General (QGEN) Survey.

Abstract

Background: Comprehensive health-related quality of life (QOL) assessment under severe respondent burden constraints requires improved single-item scales for frequently surveyed domains. This article documents how new single-item-per-domain (SIPD) QOL General (QGEN-8) measures were constructed for domains common to SF-36 and results from the first psychometric tests comparing scores for the new measure in relation to those for the SF-36 profile and summary components.

Research design: Online NORC surveys of adults, ages 19-93 (mean=52 y) representing the US population in 2020 (N=1648) included QGEN-8 and SF-36 items measuring physical (PF), social (SF), role physical (RP) and role emotional (RE) functioning and feelings of bodily pain (BP), vitality (VT), and mental health (MH). QGEN-8 items were constructed with response categories increasing score ranges for functioning (PF, SF, RP, RE) and directly measuring first-order factors for feelings (BP, VT, and MH). Analyses compared ceiling effects, convergent-discriminant correlations, classic and confirmatory factor analysis (CFA) testing for higher-order physical and mental components, and validity in discriminating across groups differing in comorbid condition severity.

Results: QGEN-8 reduced response times by 75% and lowered ceiling effect percentages (-2.2% to -27.8%, median=-14%) in comparison with SF-36. Their common measurement model was supported by: (1) substantial convergent correlations (r=0.576-0.778, median r=0.721) between methods for all domains; (2) lower discriminant correlations between different domains; (3) patterns of factor loadings equivalent to previous studies and adequate CFA model fit; (4) high correlations between methods for physical (r=0.813) and mental (r=0.761) component scores; and (5) equivalent average declines across groups reporting worse comorbid conditions.

Conclusions: Overall, results support the use of QGEN-8 to reduce respondent burden and ceiling effects while maintaining convergent and discriminant validity sufficient to estimate group-level SF-36 physical (PCS) and mental (MCS) summary scores. To facilitate its use, QGEN-8 has been made available in multiple languages from the non-profit Mapi Research Trust at https://eprovide.mapi-trust.org.