Measuring patients' views: a bifactor model of distinct patient-reported outcomes in psychosis

Abstract

Background. Patient-reported outcomes (PROs) are widely used for evaluating the care of patients with psychosis. Previous studies have reported a considerable overlap in the information captured by measures designed to assess different outcomes. This may impair the validity of PROs and makes an a priori choice of the most appropriate measure difficult when assessing treatment benefits for patients. We aimed to investigate the extent to which four widely established PROs [subjective quality of life (SQOL), needs for care, treatment satisfaction and the therapeutic relationship] provide distinct information independent from this overlap.Method. Analyses, based on item response modelling, were conducted on measures of SQOL, needs for care, treatment satisfaction and the therapeutic relationship in two large samples of patients with psychosis.Results. In both samples, a bifactor model matched the data best, suggesting sufficiently strong concept factors to allow for four distinct PRO scales. These were independent from overlap across measures due to a general appraisal tendency of patients for positive or negative ratings and shared domain content. The overlap partially impaired the ability of items to discriminate precisely between patients from lower and higher PRO levels. We found that widely used sum scores were strongly affected by the general appraisal tendency.Conclusions. Four widely established PROs can provide distinct information independent from overlap across measures. The findings may inform the use and further development of PROs in the evaluation of treatments for psychosis. Key words : Bifactor model, evaluation, patient-reported outcomes, psychosis, validity. IntroductionPatient-reported outcomes (PROs) have become increasingly important in the evaluation of treatment for patients with psychosis. A PRO can be defined as ' any report coming directly from patients (i.e. study subjects) about a health condition and its treatment ' (FDA, 2006). PRO measures can be used to assess the impact of an intervention on one or more aspects of patients' health status, hereafter referred to as PRO concepts. The term ' PRO ' has been used in an increasingly inclusive way, referring not only to purely symptomatic outcomes but also to more complex multidomain concepts such as subjective quality of life (SQOL), needs for care, treatment satisfaction, or the quality of the therapeutic relationship. For measures of multidomain concepts, a conceptual framework is generally used, in which items (e.g. satisfaction with physical health) are grouped within domains (e.g. health), and domains within more general PRO concepts (e.g. SQOL). Research evaluating treatment benefits for patients with psychosis has drawn extensively on PROs . Regulatory agencies have also proposed including well-validated PROs as effectiveness end-points in randomized controlled trials (EMEA, 2005 ;FDA, 2006). At present, in the UK, service providers are expected to use PROs for assessing the quality of routine care (DoH, 2008(DoH, , 2009.When assess...

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“…Whilst this may be seen as disappointing, it clarifies that the positive impact on SQOL and self-rated unmet needs is not just a generalised more positive appraisal across all patient-rated outcomes [31] . The effect seems to be more specific and is not primarily linked to a non-specific effect of the therapeutic relationship either.…”

Effective patient–clinician interaction to improve treatment outcomes for patients with psychosis: a mixed-methods design

“…As opposed to being disappointing, this finding suggests that the positive effect on subjective quality of life and self-rated unmet needs is not merely a generalised positive appraisal across all patient-reported outcomes. 68 On the contrary, the effect may be more specific and is not primarily linked to non-specific effects such as the therapeutic relationship. That this intervention did not have any significant effect on the therapeutic relationship also supports this.…”

The validity of subjective quality of life measures in psychotic patients with severe psychopathology and cognitive deficits: an item response model analysis

“…In such cases, one can keep the item in the instrument and adjust for DIF statistically. However, statistical adjustment for DIF requires modelbased approaches to scoring such as item response modelling and item banking, which have not yet been developed for SQOL in patients with psychosis [6,73].…”

“…health), and domains within a more general SQOL concept [2,3]. Both research studies and service providers now extensively draw on SQOL to assess treatment benefits for patients [4][5][6][7].…”