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Table 3 Fixed attributes used in DCE and rationale for inclusion

From: A novel design process for selection of attributes for inclusion in discrete choice experiments: case study exploring variation in clinical decision-making about thrombolysis in the treatment of acute ischaemic stroke

Attribute Rationale for inclusion Fixed level Rationale for level
Blood glucose level Variable levels may result in diagnostic uncertainty 6 mmol/L Average blood glucose level based on SITS data of treated patients
CT scan text description To avoid skill/subjectivity around interpretation of scans CT scan was conducted and is consistent with ischaemic stroke; it shows no haemorrhage or new ischaemic changes Decided not to include image due to potential variability in CT image interpretation skill and subjectivity; difficulty finding scans to match multitude of various patient characteristics. Text description deemed most appropriate to remove diagnostic uncertainty
To ensure confirmation of diagnosis of acute ischaemic stroke
Anticoagulation status While it was deemed an influential attribute, only minority of stroke patients take an anticoagulant and therefore it was not included as variable attribute patient is not on anticoagulation therapy To avoid any issues surrounding INR levels that could complicate the decision to offer thrombolysis
Bleeding risk / recent surgery Only relevant for a minority of patients. Challenging to operationalise variable and comparable levels in vignettes no recent history of major bleeding  
Diabetes Not ranked as important in vignettes no history of diabetes  
Included as fixed attribute for clinical validity
Patient consent/ family assent   assume either patient consent of family assent is available for treatment  
Other / Comorbidities   there are no other attributes which would deter treatment Due to difficulty defining fully and generating comparable and feasible levels of comorbidities. Potential overlap with pre-stroke cognitive and pre-stroke dependency status
Fixed attributes included post-pilot testing (Stage 4)
Handedness of patient   “All patients are right-handed” To clarify and ensure the deficits will be interpreted consistently across all level of stroke severity (NIHSS)
Licenced dose bolus preparation time   “can be prepared for administration within 5 min” Pilot testing revealed that participants would attribute in variable times in their decision-making so stating this will help control this potential error