Development and validation of the symptom burden questionnaire for long covid (SBQ-LC): Rasch analysis, 2022, Hughes et al

[Andy]

Abstract

Objective To describe the development and validation of a novel patient reported outcome measure for symptom burden from long covid, the symptom burden questionnaire for long covid (SBQ-LC).

Design Multiphase, prospective mixed methods study.

Setting Remote data collection and social media channels in the United Kingdom, 14 April to 1 August 2021.

Participants 13 adults (aged ≥18 years) with self-reported long covid and 10 clinicians evaluated content validity. 274 adults with long covid field tested the draft questionnaire.

Main outcome measures Published systematic reviews informed development of SBQ-LC’s conceptual framework and initial item pool. Thematic analysis of transcripts from cognitive debriefing interviews and online clinician surveys established content validity. Consensus discussions with the patient and public involvement group of the Therapies for Long COVID in non-hospitalised individuals: From symptoms, patient reported outcomes and immunology to targeted therapies (TLC Study) confirmed face validity. Rasch analysis of field test data guided item and scale refinement and provided initial evidence of the SBQ-LC’s measurement properties.

Results SBQ-LC (version 1.0) is a modular instrument measuring patient reported outcomes and is composed of 17 independent scales with promising psychometric properties. Respondents rate their symptom burden during the past seven days using a dichotomous response or 4 point rating scale. Each scale provides coverage of a different symptom domain and returns a summed raw score that can be transformed to a linear (0-100) score. Higher scores represent higher symptom burden. After rating scale refinement and item reduction, all scales satisfied the Rasch model requirements for unidimensionality (principal component analysis of residuals: first residual contrast values <2.00 eigenvalue units) and item fit (outfit mean square values within 0.5 -1.5 logits). Rating scale categories were ordered with acceptable category fit statistics (outfit mean square values <2.0 logits). 14 item pairs had evidence of local dependency (residual correlation values >0.4). Across the 17 scales, person reliability ranged from 0.34 to 0.87, person separation ranged from 0.71 to 2.56, item separation ranged from 1.34 to 13.86, and internal consistency reliability (Cronbach’s alpha) ranged from 0.56 to 0.91.

Conclusions SBQ-LC (version 1.0) is a comprehensive patient reported outcome instrument developed using modern psychometric methods. It measures symptoms of long covid important to people with lived experience of the condition and may be used to evaluate the impact of interventions and inform best practice in clinical management.

Open access, https://www.bmj.com/content/377/bmj-2022-070230

 

[Hutan]

Existing symptom measuring questionnaires (6 of them) were found to be inadequate:

The conceptual framework underpinning SBQ-LC was developed from systematic literature reviews of long covid symptoms.526 Existing symptom measures (n=6) with good face validity in the context of long covid were reviewed to establish whether a new instrument for symptom burden that measured patient reported outcomes was needed.202728293031 When mapped to the conceptual framework, symptom coverage of these instruments ranged from 27.0% to 60.3%: mean 34.5% (standard deviation 16.2%). Supplementary table S1 presents the concept coverage matrix mapping symptom coverage of the candidate instruments to the conceptual framework. The finding from this mapping suggested that complete coverage of long covid symptoms could not be guaranteed using existing measures, providing justification for the development of SBQ-LC.

Patient involvement

SBQ-LC was developed with the extensive involvement of adults with lived experience of long covid, and patient input is a strength of this study. Involvement of the target population is regarded as ideal in the development of instruments to measure patient reported outcomes and may be considered of particular importance in the context of long covid where the evidence base is rapidly evolving and affected individuals have reported experiences of stigma and a lack of acknowledgement from the medical community about the breadth and nature of their symptoms.10 Involvement of adults with long covid in all phases of the study (development, refinement, and validation) ensured patients’ voices were embodied in SBQ-LC’s items.

As a Rasch developed instrument, SBQ-LC’s ordinal raw scales may be converted to linear scales, with each 1 point change in a scale score being equidistant across the entire scale. Linear scores will enable the direct comparison of scores across SBQ-LC’s scales for a comprehensive assessment of symptom burden. As a multi-domain item bank, the modular construction of SBQ-LC means researchers and clinicians have the option of selecting only those scales required to provide targeted assessment of a particular symptom domain, thereby reducing respondent burden by removing the need to complete SBQ-LC in its entirety. Moreover, the Rasch model makes it possible to compare data from the SBQ-LC with other instruments measuring patient reported outcomes through co-calibration studies.

 

[Trish]

Is there any way we can access the questionnaires? I find it impossible to gauge whether this is a useful development without seeing what they developed.

 

[Lilas]

@Trish, it's in Data Supplement under " Related Content ". Here is the full document :
https://www.bmj.com/content/bmj/suppl/2022/04/27/bmj-2022-070230.DC1/hugs070230.ww.pdf

First, there is the " Clinician survey for content validation of the draft SBQ-LC item pool " (File S1), to get patient feedback on the draft, for exemple. Then, on page 33 of the Data Supplement, the "final" version 1.0 of the SBQ-LC, I suppose.

 

[Trish]

Thanks Lilas.