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. Eight deliveries from three drivers means n is…
- A. always 8
- B. always 3
- C. 8 or 3, depending on the stated unit
- D. undefined
2. df.mean() on a column with missing values…
- A. raises an error
- B. silently skips them, so the effective n is unstated
- C. returns NaN
- D. fills them with zero
3. df.duplicated().sum() == 0 on a table with repeated measurements means…
- A. the rows are independent
- B. only that no two rows are identical in every column
- C. the data is clean
- D. the unit is correct
4. In a statsmodels formula, C(plan) with levels economy, express and standard uses which reference?
- A. standard, as the obvious baseline
- B. economy, alphabetically first
- C. whichever has most rows
- D. the first in the DataFrame
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 run
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Answer Key and Explanations
Check these only after attempting every question.
1. C — 8 or 3, depending on the stated unit
The same data supports two sample sizes, and every standard error divides by the square root of n.
2. B — silently skips them, so the effective n is unstated
count() is the aggregation that reports what was actually used.
3. B — only that no two rows are identical in every column
Repeated measurements are different values from the same unit. Compare len(df) with df[unit].nunique() instead.
4. B — economy, alphabetically first
Alphabetical order puts economy first, so every coefficient silently compares against it.
5. B — a question for the data owner
A duplicated id or an undersized group will not stop ttest_ind 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.