Statistical Analysis Workflow

Quick check

A retailer asks whether a new layout increases weekly spend. Which definition states the analysis target before any calculation?

1. AA statistical question only needs a dataset and a preferred test; cases, variables, population, and estimand can all be chosen after inspecting the output.

   That reverses the workflow and permits the observed result to redefine every element of the question.

2. BA statistical question should identify the cases, the measured variables, the population of interest, and the population quantity being estimated.

   Naming cases, variables, population, and target quantity fixes what evidence and conclusion the analysis must connect.

3. CIt is enough to name the observed sample and response column, because the target population and population quantity are implied by whichever statistic is computed.

   A sample and column do not specify the group to generalize to or the population feature being estimated.

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Quick check

What is the main protection gained by writing the analysis plan before inspecting the result?

1. AAn analysis plan links the question and study design to summaries, models, diagnostics, and reporting decisions before the result is known.

   Pre-specification makes deviations visible, helping analysts explain changes without silently changing summaries or models.

2. BAn analysis plan is a record of the significant results selected after all models have been compared.

   A plan precedes results; a post hoc selection log cannot prevent outcome-driven choices.

3. CIt is the software script that runs the final test, regardless of the study question or design.

   Executable code is useful but does not itself connect the scientific target to design and reporting choices.

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Quick check

A mean looks stable but the histogram shows two separated groups. How should the analyst use both pieces of evidence?

1. AA numerical summary always contains every feature visible in a graph.

   Compression into one or two numbers can hide clusters, gaps, asymmetry, and outliers.

2. BThe graph should replace numerical summaries because a display preserves all inferential information, uncertainty, and every design qualification for the target population.

   A display reveals structure but does not supply every magnitude, precision measure, or design qualification.

3. CQuantitative summaries and graphical displays complement one another because each can reveal features the other compresses or obscures.

   Displays expose structure while numerical summaries quantify it, so the two views can reveal different defects in the same data.

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Quick check

A scatterplot shows a strong pattern in a convenience sample. Why is the graph alone insufficient for a population claim?

1. AA graph establishes the population relationship whenever the plotted sample pattern is strong.

   Visual strength in observed data cannot create representative sampling or valid assignment.

2. BA graph describes the observed data and may challenge a model, but it does not by itself justify inference beyond the design.

   A plot can diagnose the observed sample, but a population claim depends on how the sample was selected.

3. CA graph is only decoration after fitting and cannot reveal violations of model assumptions or data-quality problems.

   Plots can diagnose structure and model mismatch even though they cannot establish inferential scope.

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Quick check

The target is median customer spend and the file contains repeated rows per customer, but an analyst selects the first software procedure for independent means. Which ordering principle was violated?

1. AThe analyst should run every available procedure, retain the one with the smallest p-value, and redefine the research question to match that output.

   This makes method availability and observed results determine the target, creating analytical drift.

2. BThe most familiar software command should determine the model even when its assumptions conflict with the sampling and measurement process.

   Familiarity does not make a procedure answer the intended question or fit the generating process.

3. CThe research question and data-generating process should determine the method, rather than the list of procedures available in software.

   This ordering helps analysts notice when software availability changes the scientific target after they see the data.

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Quick check

A convenience sample yields a small positive estimate with a narrow interval, while diagnostics show model mismatch. Which elements must the final conclusion include?

1. AA qualified conclusion reports the estimated magnitude, its uncertainty, the population and conditions covered, and the assumptions that matter.

   Those elements state what was estimated, how uncertain it is, and exactly where the claim ceases to apply.

2. BA qualified conclusion reports only whether a conventional significance threshold was crossed.

   A threshold omits magnitude, uncertainty, scope, and assumptions.

3. CIt reports the sample estimate as a universal fact.

   A sample result without population and design limits overstates the evidence.

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