C48 · Topic 3.16 · 40 minutes · AAP-3.F
Investigate sensitivity and model limits
By the end you can:
- Compare capacities while holding demand fixed.
- Choose an output relevant to a stakeholder.
- Evaluate predictions against assumptions and real observations.
Before this lesson: topics 3.8, 3.15.
- Simulation
- A model that imitates selected features of a process.
- Assumption
- A condition treated as true by the model that may simplify reality.
Understand
Change one parameter while holding other inputs fixed to investigate its effect. This controlled comparison helps isolate the parameter, but does not prove a causal claim about an unobserved real population. Validate the model with appropriate observations.
A deterministic simulation repeats the same result for identical inputs. A model with random arrivals can vary; repeated runs describe variability rather than guarantee one exact outcome. More computational detail does not automatically make a model more accurate if its assumptions are wrong.
Worked example
Compare capacity 2 and 3 using the same four-tick arrivals[3,0,4,1].
- Capacity 2 ends with 1 waiting and 7 served. Capacity 3 ends with 0 waiting and 8 served.
- This predicts an improvement under the stated rules, but does not estimate labour cost or actual waiting times.
- A counterfactual with different arrivals would confound a simple capacity comparison.
Explore each concept
Choose a concept, change its inputs and follow the explanation. Each example models the stated rule or scenario; completing it is practice rather than evidence of mastery.
- Abstraction and omitted factors
- Arrivals before or after service
- Controlled comparison and variability
Change it · step through · explain
Change an input, predict what will happen, then advance one step. Read why the state changes, reset and experiment. This fixed teaching model does not save progress or award XP.
Ready · Make a prediction
- Arrivals per tick (0–100; max 8)3,0,4Waiting
- Capacity per tick (0–10)2Waiting
- Event orderarrivals-firstWaiting
Ready to explore: Simulation assumptions and event order
Why: Change an input, predict the first effect, then advance one step.
Try this: Change one input or choose another listed case. Predict the effect, reset and compare the states and governing rule.
Step through and experiment
Change it · step through · explain
Change an input, predict what will happen, then advance one step. Read why the state changes, reset and experiment. This fixed teaching model does not save progress or award XP.
Ready · Make a prediction
- Input 13,0,4,1Waiting
- Input 22Waiting
Ready to experiment
Why: Predict the first change, then advance one step.
Try this: Try capacity 0 and an empty arrivals list. Try a busy tick followed by zero arrivals.
Check a misconception
Claim: A model prediction proves that a proposed real intervention will work.
The prediction depends on assumptions and data; validate and consider outcomes the model omits.
Guided practice
Suggest an extra output that helps evaluate crowding, and compute it for capacity 2.
Work with a partner. Make a prediction, compare your reasoning, then identify the rule that supports your answer.
Independent transfer
The real desk has different service times. Propose one model improvement and one added cost.
Exit check
Why should two staffing comparisons use the same arrival sequence?
Write your reasoning before comparing with a classmate. If your teacher assigned this task, submit it through My classes to save your work and receive feedback.
Check yourself
Your practice so far
Check an answer to see its rationale.