Portfolio Variance Quant Interview Guide
Portfolio variance quant interview guide for covariance terms, diversification, risk intuition, examples, and common calculation mistakes.
Candidates preparing for risk, covariance, and portfolio construction prompts.
Portfolio variance includes covariance
Portfolio variance is not just the weighted average of individual variances. Covariance terms determine how positions move together and often drive the diversification benefit.
Correlation shapes combined risk
If assets are imperfectly correlated, combined risk can be lower than the sum of standalone risks. If correlations rise together, diversification can disappear when it is most needed.
Concrete example
Two equal-size positions with low covariance can reduce portfolio variance compared with two highly correlated positions. The same standalone volatility can produce different portfolio risk.
Use units and weights carefully
Weights, volatility units, and covariance scale must match. A common interview error is mixing percent returns, decimal returns, and annualized numbers without saying what is being used.
Common mistakes
Candidates often forget the covariance term or assume correlation is constant. A stronger answer explains the formula and then asks whether the dependence estimate is stable.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.