Derive Coefficient and Covariance in Regression Analysis
Company: Citadel
Role: Data Scientist
Category: Statistics & Math
Difficulty: medium
Interview Round: Technical Screen
##### Scenario
Assessing knowledge of correlation structure, regression relationships and covariance calculations.
##### Question
1) For three random variables X, Y, Z with identical pairwise correlations ρ, what is the smallest possible value of ρ?
2) In simple linear regression of Y on X, you know R² and the slope coefficient β(y|x). Derive the slope β(x|y) from regressing X on Y.
3) Let X and Y be i.i.d. Uniform(0, 1). Compute Cov(max(X, Y), min(X, Y)).
4) Given a monotone function Y = g(X), derive the pdf of X from the pdf of Y (inverse-function distribution).
##### Hints
Use positive-definite covariance matrices, β relations with R², Cov identities, and change-of-variables theorem.
Quick Answer: This question evaluates competency in probabilistic reasoning and regression analysis, including correlation constraints, relationships between regression slopes, covariance of order statistics, and change-of-variables for transformed random variables.