Module 02 Knowledge Check
5 questions. Pass mark 4 out of 5. Answer every question before checking the answer key below, then retry after reading the feedback.
1. Six rows from three users means n is…
- A. always 6
- B. always 3
- C. 6 or 3, depending on the stated unit of analysis
- D. undefined
2. Missingness that is unbalanced between groups is…
- A. harmless if under 10%
- B. evidence that it may not be random
- C. corrected automatically by na.rm
- D. only a problem for categorical data
3. Treating three measurements from one person as three independent observations…
- A. widens the confidence interval
- B. narrows the interval beyond what the data earns
- C. has no effect on the interval
- D. is corrected by the t-test automatically
4. If a trial's arms are named placebo, dose_low and dose_high, R's default reference is…
- A. placebo, as the obvious control
- B. dose_high, alphabetically first
- C. whichever has most rows
- D. chosen at random
5. A failed pre-test check on the analysis table should lead to…
- A. relaxing the check
- B. a question for the data owner
- C. deleting the offending rows
- D. proceeding, since the test will still run
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Answer Key and Explanations
Check these only after attempting every question.
1. C — 6 or 3, depending on the stated unit of analysis
The same data supports two sample sizes, and every interval and p-value depends on which one you meant.
2. B — evidence that it may not be random
Complete-case analysis assumes missingness is unrelated to the outcome. An imbalance is evidence against that.
3. B — narrows the interval beyond what the data earns
It inflates n, shrinks the standard error and always makes the result look stronger. In the lesson the interval was 60% too narrow.
4. B — dose_high, alphabetically first
Alphabetical order puts dose_high first, so every coefficient silently compares against the highest dose.
5. B — a question for the data owner
A duplicated id or an undersized group will not stop t.test() returning a confident answer.
Practical Check
Apply this module to your own work: complete the module activity for *Preparing Data for Statistical Analysis*, then write one sentence naming what your result shows and one naming what it does not.
Strong Answer Pattern
A strong answer names the task, the evidence used, the check performed, and the remaining limitation. It avoids "proved", "guaranteed", or "always" unless the evidence genuinely supports it.