Table 1

General factors used in rheumatology workforce studies

Author, year	Country	Model¹	Time horizon²	Update of the model³	Assessment of model performance⁴	Uncertainty analyses⁵	Regional heterogeneity⁶	Stakeholder involvement⁷
Ogryzlo, 1975²⁶	USA Canada	Needs based	5 years	No update	No assessment	Not performed	Outlying communities and many urban centres (with population exceeding 100 000) do not have enough rheumatologists	Not stated
Marder et al, 1991¹⁴	USA	Need, demand and supply based, assumed demand≠supply at baseline	10 and 20 years	No update	No assessment	Most conservative estimate calculated based on (1) simultaneity adjustment (1.25); (2) productivity factor (5000 visits/year); (3) decrease in need of other medical visits. Result: twice as high need of rheumatologists	Not stated	Not stated
Deal et al, 200715	USA	Need, demand and supply based, assumed demand=supply at baseline	20 years with predictions for 5-year interval	Update performed in 20154	Assessment performed in the update of 2015	Tested decline in people without insurance and a higher increase in income	Not stated	Involved an advisory panel including physicians and health professionals
Zummer and Henderson, 200018	Canada	Need and supply based	Baseline only	No update	No assessment	Not performed	Not stated	Not stated
Edworthy, 200019	Canada	Need, demand and supply based, assumed demand≠supply at baseline	10 years	No update	No assessment	Not performed	Not stated	Not stated
Hanly, 200120	Canada	Need and supply based	25 years with predictions for 5-year interval	No update	No assessment	Not performed	Not stated	Not stated
Raspe, 1995²²	Germany	Need, demand and supply based, assumed demand=supply at baseline	Baseline only	No update	No assessment	Not performed	Not stated	Not stated
German Society for Rheumatology, Committee for Care, 2008²¹	Germany	Need, demand and supply based, assumed demand=supply at baseline	Baseline only	Update performed in 2017	No assessment	Not performed	Not stated	Not stated
Làzaro y De Mercado et al, 201325	Spain	Need, demand and supply based, assumed demand=supply at baseline	11 years	No update	No assessment	Base scenario: Increased demand (15%) due to population growth and increased demand in care Best scenario: increase in demand only due to population growth Worse scenario: increase in demand (30%) due to population growth and increased demand for healthcare	Not stated	Not stated
Committee of Rheumatology, 1988²³	UK	Need and supply based	Baseline only	No update	No assessment	Not performed	Many counties of the UK are lacking rheumatological service	Not stated
Rowe et al, 2013²⁴	UK	Need, demand and supply based, assumed demand≠supply at baseline	Baseline only	No update	No assessment	Not performed	Input data will change based on regional variations in patient demographics and models of care	Not stated
American College of Rheumatology, 2015³⁸	USA	Need, demand and supply based, assumed demand≠supply at baseline	15 years with predictions for 5-year interval	NA, too recent	Assessed against study of 200515	Best-worse scenario: Male-female ratio in workforce Retirement projections Full- and part-time projections Academic vs non-academic setting Number of new graduates Number of non-physician providers (NP and PA) Number of patients with OA seen by rheumatologists	Is assessed at baseline (2015) for 10 regions of USA, and separately for the 10 largest metropolitan areas No change in geographic services in the next 10 years is assumed Physicians practicing in metropolitan statistical area work on average 15% less hours than those not working in these areas	Multidisciplinary expert group: eight core members and additional expert liaisons made up of various affiliations and disciplines to ensure a wide-range of ideas and experiences in the field of rheumatology; focus groups with select stakeholders (not stated which)
HRSA Health Workforce, 2015¹⁶	USA	Need, demand and supply based, assumed demand=supply at baseline	12 years	NA, too recent	Face validity by experts, internal validation (verification, including ‘stress test’ for extreme values), external and predictive validation against other (not used in modelling) data sources, between model validation (with results of other models)	Not performed	Separate estimates for four regions, baseline supply≠to baseline demand in regions	Not stated
German Society for Rheumatology, 2017⁷	Germany	Need, demand and supply based, assumed demand=supply at baseline	Time horizon not provided for all aspects	NA, too recent	Assessed against study of 20089	Not performed	General regional deficit of 0–1, 2 rheumatologists/100 000 inhabitants	The study group consisted of rheumatologists (ambulant/inpatient, rehabilitative setting), epidemiologists and members of the German Rheumatology Society

The risk of bias scores: red dot ()=high risk of bias, indicating that the factor has not been considered or considered in an inadequate way, in workforce prediction model; orange dot ()=moderate risk of bias, when a factor has been considered with limitations; green dot ()=low risk of bias and corresponds to a well-considered factor in sufficient level of detail and based on a reliable evidence. Detailed description of grading system is presented in online supplementary table S7.
(1) For the most accurate prediction, a model should consider supply, need and demand factors and not assume that demand is equal supply at the baseline.
(2) Predictions between 5 and 15 years seem to be the most adequate time horizon for workforce calculation in rheumatology.
(3) Frequent updates of the model (1-year to 4-year interval) should be done in order to take into account the variability of assumptions.
(4) At least two kinds of quality assessment for baseline calculations and/or for future predictions are recommended.
(5) Uncertainty analyses with more than two parameters are recommended in order to detect assumptions that may vary due changes.
(6) Predictions should consider the relevant regional profile of the country.
(7) The involvement of more than one group of stakeholders is highly relevant for all stages of the prediction.
HRSA, Health Resources and Services Administration; NA, not applicable; NP, nurse practitioner; OA, osteoarthritis; PA, physician assistant.