Table 1

Population, cost and capacity inputs for BaS scale-up model

	Model input	Source
(A) Population inputs
Total population (≥18 years age)	44 715 345	44
Proportion of population eligible for BaS (NICE guidelines)	7.78%	45
Obesity incidence rate (annual)	2.97%	6
Prevalent population (NICE guidelines eligibility criteria)	3 478 854	6
Incident population (annual) (NICE guidelines eligibility criteria)	103 261	6
Proportion of eligible population that is estimated to receive BaS*	10.00%	Assumption
Estimated current eligible population size†	347 885	Calculated
Estimated newly eligible population size (annual)‡	10 326	Calculated
(B) Cost inputs
Inputs	Source
Cost per procedure for gastric band, sleeve gastrectomy and gastric bypass§	NHS reference costs46
Complication treatment costs (cost per episode for cholecystectomy, abdominal wall hernia operations, banding operations, leakage and abscess, obstruction, stricture, gastric ulcer)	NHS reference costs46
Cosmetic surgery cost	Excluded from cost inputs
Cost per episode for gastric ulcer (included 8-week antibiotics treatment, one GP visit and one diagnostic test)	NHS reference costs46
Infrastructure costs for BaS scale-up (small-scale and large-scale facilities): Number of BaS procedures per year (facility capacity). Cost of setting up facility. Time required to set up the facility (in years). Time required for facility to be fully functional (in years).	PMR KDMs’ interviews¶
(C) Capacity inputs
Inputs	Source
Current annual capacity (number of BaS) for NHS and private sector**	PMR KDMs’ interviews¶47
Maximum potential annual capacity	PMR KDMs’ interviews¶
Current BaS distribution by procedure type (gastric band, sleeve gastrectomy and gastric bypass) for 2013–2018	34
BaS distribution by procedure type (for scale-up strategy)††	Inputs from bariatric surgeons¶

Among five KDMs, three were heads of the departments (gastroenterologist, two were the lead for BaS), one was C-level executives/board member of a hospital and one was the director of procurement.
*There are several reasons why a patient may not receive BaS despite being eligible; these include (but are not limited to) patient preference, physician preference/attitude towards BaS, along with costs and waiting lists.
†Calculated using prevalent population keeping proportion of eligible population who receive BaS as 10%.
‡Calculated using incident population keeping proportion of eligible population who receive BaS as 10%.
§All the resource costs incurred at every stage of the patient pathway were assumed to be included in the procedure for all eligible costs patients.
¶Data from PMR report are described in online supplemental table 1.
**2018–2019 data are included; 2020–2022 data are excluded since numbers were under-represented due to COVID-19 pandemic.
††Based on bariatric surgeons’ opinion that the gastric band procedure is the least effective BaS and is assumed to be gradually phased out in next 10 years.
BaS, bariatric surgery; KDMs, key decision-makers; NHS, National Health Service; NICE, National Institute for Health and Care Excellence; PMR, primary market research.