Transcript Slide 1
Scenario Generator: Health Services simulation Why simulate? • Go beyond a process map into potential impacts of implementation • Aids understanding of complex systems • Discover unanticipated consequences of a plan BUT • Simulation won’t tell you the answer, but it will help you ask better questions • It will only be as good as the data you put in, but it will help you make sense of that data • All models are wrong, but some are useful • It will not be an accurate predictor of events, but it might be better to be “broadly right than precisely wrong” Main simulation approaches Modeling Method What is modeled Continuous Discrete event Discrete rate Processes Individual items Flows of stuff Examples Processes: chemical, biological, economic, electronics. Things: traffic, equipment, work product, people. Information: data, messages, and network protocols at the packet level. Rate-based flow of stuff: homogeneous products, high speed production, data feeds and streams, mining. What causes a change in state Time steps A time change An event An event Interval between time steps is constant. Model recalculations are sequential and time dependent. Interval between events is dependent on when events occur. Model only recalculates when events occur. Characteristics of what is modeled Track characteristics in a database or assume the flow is homogeneous. Using attributes, items are assigned unique characteristics and can then be tracked throughout the model. Interval between events is dependent on when events occur. Model only recalculates when events occur. Track characteristics in a database or assume the flow is homogeneous. Statistical detail General statistics about the system: amount, efficiency, etc. In addition to general statistics, each item can be individually tracked: count, utilization, cycle time. In addition to general statistics, effective rates, cumulative amount. Simulation modelling in NHS • Very few simulation tools available used in a healthcare setting • Key commercial tools used within NHS environment: – Simul8 (Discrete Event approach) – Isee systems - STELLA/iThink (Continuous approach) – ExtendSim (Multiple methodologies – continuous or discrete) Features of Scenario Generator • Discrete event simulation applied to a strategic planning domain • No programming skills needed • Introduces element of randomness (stochastic process) • Allows simulation of a suite of care pathways running simultaneously • Supports reiteration of decisions over time Functional model Population Demography Prevalence Scenarios Referral patterns Capacity Duration Events Population Demographic weighting Prevalence Mental Health Urgent Planned Whole system model Simulation results Pathway models Constrained resources Maternity Service points, flows & waits Capacity & Constrained Resources • Resources can be configured that have – event duration, inherited from actual step or user defined – number of queues • A constrained resource can be associated with any pathway steps across all pathways in the model • A pathway step can be associated with one resource (or none) • Events reaching constrained resources are distributed randomly to queues. Ideal project team in use: Scenario Generator • Have some idea of the problem you are addressing • Identify your principal customer / stakeholder • Draw together a core team – leadership – a champion senior clinician or executive manager – service design / improvement lead – commissioning lead – public health lead / analyst – finance lead – information analyst • Develop a collaborative approach • Work within an overall change programme Define problem Design initial model Select approaches Develop concept Do Do other analys analyses es Validate Refine Simulate Draw conclusions Consult Act upon outputs Draft Outcomes ver 4.2 Rehabilitation activity and estimated running costs when comparing a baseline and intervention models, 2008 Inpatient Strokes acute costs Maximum acute bed occupancy Hospital based rehab (up to 6 weeks) Maximum rehab bed occupancy ESD rehab @ 12 weeks (Surrey example costs) Baseline Activity Cost 351 £1,116,882 16 284 £539,600 22 £1,656,482 Intervention Activity Cost 351 £1,116,882 16 183 £285,060 18 106 £178,080 £1,580,022 Baseline of Rehabilitation Stroke unit rehabilitation Other rehabilitation Est bed days 0 9088 9088 Max bed occupancy 0 22 22 ALOS 25 32 Est bed days 3545 1248 Max bed occupancy 12 6 Intervention 36 67 Reduction -19% -28% Activity 0 284 ALOS 25 32 Activity 144 39 106 4262 4793 Baseline 45 94 Early supported discharge team in place Stroke unit rehabilitation Other rehabilitation Early supported discharge Reduction in average bed days: Outcomes Expected institutionalisation Expected early deaths after treatment Wirral PCT Primary Care Advice Lack of CAB capacity Queue size - Follow up CAB appointments 600 N people in queue 500 3 day wait 400 7 day wait 10 day wait 300 14 day wait 200 100 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month • Solution: CAB staff see 21 instead of 18 clients per week OR increase • staff by 1 FTE • Led to additional resource for CABs, determined by population need (IMD)