The average improved
Average waiting time fell to ten days, proving that the pilot worked.
The case
A fictional pilot reports ten days' mean wait for eighty completed cases. Twenty cases transferred elsewhere have a mean wait of fifty days, measured on the same basis. The report excludes them. There is no comparable baseline covering both groups.
Try it before reading on
Calculate the combined mean. State what this correction does and does not tell you about the pilot.
Use paper or your own notes. Keep the first answer as well as any revision.
Compare your reasoning
The combined mean is (80 × 10 + 20 × 50) / 100 = 18 days. Averaging the two means equally would give thirty and would be wrong here. Eighteen corrects this supplied reporting boundary. It does not establish improvement or deterioration without a comparable baseline, nor prove causation. Examine distributions, who waited, transfer appropriateness, and alternative explanations.
When could the claim be defensible?
If the groups had equal numbers and comparable definitions, the unweighted average of their means would equal the combined mean. That condition does not hold in this case.
Change the conditions
Transferred cases include time before transfer; the ten-day measure starts after triage. Can you still combine them?
Compare the changed case
Not as a comparable end-to-end wait. Align start and end definitions or present the measures separately with their limitations. Arithmetic cannot repair incompatible meanings.
Follow the specific connection
Evaluation and reflexivity: test the claim you are tempted to make
A basic mixed-evidence evaluation rehearsal. It is not a complete impact evaluation, statistical inference course or assessment of real practitioner behaviour.
System Dynamics: build, calculate and challenge a queue model
An original discrete-time stock-flow rehearsal with a deliberately simple boundary. It is not a prediction of a real service and does not validate a model merely because it runs.
Source routes and reading limits
The methodological route below uses the existing practice pack's checked resource descriptions. This release does not claim fresh reading of the external works.
UK Government: introductory systems thinking toolkit
Select the named tool, try the associated template and compare with the example. Use the pack's explicit checks where the toolkit provides no answer key.
Existing check: HTML toolkit inspected, including mapping, stock-flow, theory of change and evaluation sections. Its examples are not automatic validation of a learner's model.
Deming Institute: PDSA cycle
Write a prediction before a change and compare observation with it. The service and evaluation cases here give a small exercise and answers.
Existing check: The Institute's account of prediction, study and theory revision inspected. It distinguishes PDSA from a simple implementation check.
Wenger-Trayner: systems convening, free book and resources
Use the cases to examine legitimacy, boundaries, agency and learning partnerships. The original case here provides the checkable rehearsal.
Existing check: Authors' page, free PDF route and paperback links inspected. It is a related social-learning resource, not identical to every method grouped in the bridge exercise.
MIT: System Dynamics Self Study, assignments and solutions
Start with the early assignments and their paired solutions. Predict behaviour, calculate it, then compare. Do not confuse this course with MIT courses that publish assignments without solutions.
Existing check: Assignment/solution pairs on the MIT page inspected. Historic software instructions may need adaptation; the whole course was not executed.
Take one revision away
Write the claim you can now support, the assumption you changed, and the observation or decision still needed. Do not turn the worked comparison into a compulsory answer where the question admits alternatives.
Choose another claim · Print all task sheets · Download the cases and route record