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Probability and Statistical Inference Questions

Covers fundamental probability theory and statistical inference from first principles to practical applications. Core probability concepts include sample spaces and events, independence, conditional probability, Bayes theorem, expected value, variance, and standard deviation. Reviews common probability distributions such as normal, binomial, Poisson, uniform, and exponential, their parameters, typical use cases, computation of probabilities, and approximation methods. Explains sampling distributions and the Central Limit Theorem and their implications for estimation and confidence intervals. Presents descriptive statistics and data summary measures including mean, median, variance, and standard deviation. Details the hypothesis testing workflow including null and alternative hypotheses, p values, statistical significance, type one and type two errors, power, effect size, and interpretation of results. Reviews commonly used tests and methods and guidance for selection and assumptions checking, including z tests, t tests, chi square tests, analysis of variance, and basic nonparametric alternatives. Emphasizes practical issues such as correlation versus causation, impact of sample size and data quality, assumptions validation, reasoning about rare events and tail risks, and communicating uncertainty. At more advanced levels expect experimental design and interpretation at scale including A B tests, sample size and power calculations, multiple testing and false discovery rate adjustment, and design choices for robust inference in real world systems.

EasyTechnical
1 practiced
You observe two features: X and Y. Explain what statistical independence means. Provide a clear example where two variables are marginally independent but become dependent after conditioning on a third variable Z (i.e., collider or confounder example).
HardTechnical
0 practiced
Discuss how to perform and interpret a power analysis for detecting small effect sizes in high-dimensional experiments (e.g., hundreds of metrics tracked). Include discussion of practical constraints like traffic, multiple testing, and metric correlations.
EasyTechnical
0 practiced
Define expected value, variance, and standard deviation. For a discrete random variable X taking values {0,1,2} with probabilities {0.2, 0.5, 0.3}, compute E[X], Var(X), and SD(X). Explain how variance differs from mean absolute deviation and why variance uses squared deviations.
MediumTechnical
0 practiced
You need to choose between using a z-test and a t-test to compare the means of two independent groups (A and B) in an online experiment. Group sizes are 10,000 each, but the distributions are slightly skewed. Which test would you use and why? What additional checks would you perform?
HardTechnical
0 practiced
You suspect data collection bias where certain user segments are underrepresented. Explain how to test for sampling bias statistically and one method to adjust analyses or model training to account for unequal representation.

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