Background: A short instrument would enhance the viability of a study. Therefore, we aimed to shorten the specific module (SPD-10) of the Quality of Life Instrument for Chronic Diseases - Chronic Renal Failure (QLICD-CRF) for assessing the quality of life of patients with chronic renal failure.
Methods: The 10-item SPD-10 was self-administered to 164 patients with chronic renal failure. A shortened form was first obtained by a tandem use of the classical test theory (CTT), the generalizability theory (GT), and the item response theory (IRT). In addition, we also shortened the SPD-10 by the Optimal Test Assembly (OTA).
Results: Both the tandem use of GT, CTT and IRT, and the OTA derived the same 7-item shortened version (SPD-7). It included items CRF1, CRF2, CRF3, CRF4, CRF6, CRF8, and CRF9 of the SPD-10. The SPD-7 had a Cronbach alpha of 0.78. The correlation coefficients of its total and factor scores with those of the SPD-10 were 0.96 and 0.98, respectively. Confirmatory factor analysis confirmed the unidimensional structure of the SPD-7, with the comparative fit index=0.96, the Tucker-Lewis index=0.94, and the root mean square error of approximation=0.09.
Conclusion: The short-form SPD-7 is reliable and valid for assessing the impact of clinical symptoms and side effects on the quality of life of patients with chronic renal failure. It is an efficient option without compromising the measurement performance of the SPD-10.
Keywords: Classical test theory; Generalizability theory; Item response theory; Optimal test assembly; Scale reduction.
© 2022. The Author(s).