review

Module 04 Self-Test

State what a p-value means in one sentence.
Type I vs Type II — which is the false positive?
Write a self-join to find employees who report to the same manager.
df.loc[0:3] vs df.iloc[0:3] — how many rows each?
What's the SettingWithCopyWarning and how do you fix it?
Normalized vs denormalized database — which for analytics and why?

Practice Questions

Q: State what a p-value means in one sentence.

Q: Type I vs Type II — which is the false positive?

Q: Write a self-join to find employees who report to the same manager.

A: SELECT a.name, b.name FROM employees a JOIN employees b ON a.manager_id = b.manager_id AND a.employee_id < b.employee_id (the < avoids duplicates and self-pairs)

Q: df.loc[0:3] vs df.iloc[0:3] — how many rows each?

A: loc[0:3] = 4 rows (labels 0,1,2,3 — inclusive). iloc[0:3] = 3 rows (positions 0,1,2 — exclusive end).

Q: What's the SettingWithCopyWarning and how do you fix it?

A: Chained indexing (df[...][...] = val) may modify a copy. Fix: use df.loc[condition, column] = val.

Q: Normalized vs denormalized database — which for analytics and why?