Deliver an analysis another person can inspect

The capstone brings the course together. You are an analyst advising the fictional Northstar Dispatch manager. The manager wants to choose the next operational investigation and decide whether the checklist deserves a real field pilot. The supplied shipments and simulated trial are the only quantitative evidence available. You must use their strengths without pretending they contain evidence they do not have.

A successful submission is not a gallery of every statistical technique in the course. It is a coherent answer to a bounded decision, with enough supporting detail for another learner to check it. You can complete the required work with a calculator, a spreadsheet and the supplied data. Python is an optional reproducibility route, not a hidden entrance requirement.

Stage 1 Define the question before opening the answer key

Write the population, unit, period and outcome for each part of the task. Identify what “late” means and which file supports description versus simulated experimental inference. Record the fictional manager's threshold of a 2-minute mean reduction for a potentially worthwhile checklist improvement. Treat that threshold as supplied before the analysis, not as a line you can move after seeing results.

Choose one additional question to explore within the shipment data, such as whether late rates differ by service or whether rating response varies with late status. Label it exploratory and define the denominator. A good question can reveal a limitation rather than produce a new recommendation.

Save this short plan before calculating. In real work, a written plan helps distinguish expected analyses from opportunistic searches. Here, it gives you a record you can compare with the final report. If the plan changes for a legitimate reason, retain the original and explain the revision.

Stage 2 Reconcile and summarize

Preserve the raw export. Apply or inspect the documented validation policy and reconcile its 248 records to 240 accepted shipments, three duplicates and five invalid extras. Show that normalized formatting and recomputed late flags do not create extra shipments. Include the missing-rating count separately because a missing optional rating does not invalidate a shipment's timing record.

Calculate the overall late rate and hub counts, then compare actual-time summaries with route and service mix. Use at least one distribution summary beyond the mean. State the quartile convention if you report an IQR. Investigate a surprising value instead of deleting it solely because it is inconvenient.

For a calculator or spreadsheet route, show formulas and a small row-level spot-check. For Python, write or adapt your own analysis in the learner starter and record how to run it. Running the reference program verifies the package, not your understanding.

Stage 3 Make the statistical argument

Calculate the checklist-minus-control difference, its compatible 95% Welch interval and the two-sided p-value. The supplied method output may be used if you cannot compute the distribution functions by hand, but you must show the group summaries, effect direction and interpretation. Explain the independence and model assumptions and why the trial is different from the observational shipment file.

Compare the interval with both zero and the −2-minute threshold. State what has and has not been established. Do not convert the simulated result into a claim about real workers. Do not use a non-significant hub comparison to announce equality. A decision memo can honestly say that the current evidence is insufficient for a stronger commitment.

Stage 4 Design for a reader

Prepare two charts that answer different questions. At least one must show the trial effect and its uncertainty, rather than just the two group means. The other should support the operational investigation you recommend. Give each a readable title, labels, units, population, count and accessible text description. Put exact plotted values in a nearby table or appendix.

Write a 250–400-word management brief. It should lead with the recommendation, then provide evidence and the limitation most likely to change that recommendation. Add a short methods appendix with data policy, calculations, assumptions and reproducibility details. A headline that cannot survive the appendix needs revision.

Stage 5 Ask a skeptical reviewer to reproduce it

Use the rubric in the capstone brief. A peer should be able to trace every headline number to a definition and source file. Ask the peer to find your most consequential assumption and propose a plausible condition under which your recommendation would change. Fix the substance before polishing typography.

The public learner checker, when used, checks selected arithmetic and labels in your own result JSON. It cannot judge whether your story is honest or whether a chart is accessible. The reference test suite checks the supplied implementation. Neither is an automatic course grade. The rubric includes reasoning and communication precisely because a technically correct number can support a misleading claim.

After reviewing a worked solution, close it and explain your own conclusion aloud without looking. Then answer a transfer question: if the same 40 outcomes came from four people measured ten times each, what would have to change? If your answer is “nothing, the row count is still 40,” return to independence and study design before submitting.

Attempt Practice 12A–12C, complete the staged capstone and use the self-review checklist. The suggested study times are provisional design estimates; no beginner pilot has established that this pacing works for every learner.