Statistics · Module 3Module material
Probability interview questions
26 questions interviewers ask on this module’s topics, from first principles to the follow-ups. Each comes with a model answer.
Events and probability
- What is a sample space, an event and an empirical probability?●
- How do you get the probability of "A or B" from counts?●
- What is the complement of
Amount > 100, and why does the boundary matter?● - An amount rule captures 26.4% of labelled frauds. Is it a good fraud screen?●●
- What does the law of large numbers say, and what does it not say?●●
Conditional probability and independence
- What is a conditional probability?●
- Why are P(spam | flagged) and P(flagged | spam) different?●
- How do you test whether two events are independent?●●
- Are mutually exclusive events independent?●●
- What does Naive Bayes assume about independence, and how would you check it?●●
Bayes' theorem
- State Bayes' theorem in words.●
- A test catches 90% of positives with 10% false positives. Why can most of its positives be false?●●
- What is the law of total probability, and where does it appear in Bayes' theorem?●●
- Which improves a detector's posterior more at a 1% prior: fewer false alarms or a higher catch rate?●●
- Three separate flags fire. How do you update, and when is the update wrong?●●
Random variables, expectation and variance
- What is a random variable?●
- What is an expected value, and how is it computed from a distribution?●
- How would you choose between two decision rules with different error types?●●
- The cost matrix is uncertain. How do you report the decision?●●
- Why report a variance or standard deviation with an expected cost?●●
- What is the difference between a discrete and a continuous random variable?●●
Monte Carlo simulation
- What is a Monte Carlo simulation?●
- How do you check that a simulation is working before trusting it?●●
- Why evaluate every candidate on the same simulated periods?●●
- What is the difference between Monte Carlo error and assumption uncertainty?●●
- A simulation input contains one extreme recorded day. What do you do?●●