Abstract
BackgroundThe aim of the current study was to evaluate the structural validity of the 20-item long-term conditions questionnaire (LTCQ) and to explore a potential short-form version of the scale using Rasch analysis.MethodsData were collected through postal surveys (February 2016–January 2017) from a sample of 1,211 participants diagnosed with at least one long-term condition (LTC). Identified participants were invited through either local authorities for a social care cohort (n = 294) or primary care practices for a health care cohort (n = 917). Participants were mailed a survey, including the LTCQ, demographic questions, a comorbidities measure, and other validated outcome measures. Respondents were invited to complete a follow-up survey including the LTCQ for assessment of reproducibility.ResultsThe main assumptions of the Rasch model from the LTCQ were fulfilled, although infit and outfit indices indicated some items showed misfit. Misfitted items, items that did not have a preceding set or showed some local dependence were removed one at a time, with the remaining candidate items to form an 8-item short version, the LTCQ-8. The Rasch model for the LTCQ-8 explained 64% variance and had a reliability estimate greater than 0.80. Several items in the LTCQ showed uniform differential item function (DIF) in relation to the number of reported LTCs, age, cohort and type of LTCs, but fewer items exhibited DIF in the LTCQ-8. Spearman’s rho correlations between the LTCQ and the LTCQ-8 were strong across the total sample and various subgroups. Correlations between the LTCQ-8 and all reference measures were moderate to strong, and comparable to correlations found between the LTCQ and these measures.ConclusionsThe LTCQ measures a unidimensional construct, and it is therefore acceptable to use a summed total score. The LTCQ-8 also met the assumption of unidimensionality and had comparable construct validity with the LTCQ. Additional validation is required in an independent sample.
Highlights
Over 15 million people in England (30% of the population) report having at least one long-term condition (LTC) and are major users of health and social care services [1]
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patient-reported outcome measures (PROMs) are routinely used in clinical trials and intervention studies to evaluate patients’ health status and health-related quality of life (HRQoL) [7]
Summary
Over 15 million people in England (30% of the population) report having at least one long-term condition (LTC) and are major users of health and social care services [1]. There are two types of PROMs widely indexed within the literature: disease-specific and generic PROMs. There are two types of PROMs widely indexed within the literature: disease-specific and generic PROMs The former focus on assessing health outcomes of a specific condition, whereas generic PROMs assess general aspects of functioning and/or well-being and can be used across different patient populations. Existing generic PROMs, such as the SF-36 or EQ-5D, are applicable across different populations; they do not fully capture outcomes that are important in LTCs and may not be appropriate for long-term monitoring of LTCs, for conditions where aspects of HRQoL, such as functional status, might be expected to decline over time [9, 10]. The aim of the current study was to evaluate the structural validity of the 20-item long-term conditions questionnaire (LTCQ) and to explore a potential short-form version of the scale using Rasch analysis
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