The The Voleon Group ML Research Phone interview is stage 4 of 7 in the The Voleon Group interview process, after the Onsite / VO. Format: ~60 min · stats + ML. Stats + ML phone after a reading list (~10 intro, 40 tech, 10 Q&A): OLS closed form, when (XᵀX)⁻¹ exists, gradient-descent least squares in basic numpy, R²-combining, Y~X vs X~Y slope puzzles, E[X|X+Y] for joint normals.
Preparing for this round? Practice the 23 questions mapped to the The Voleon Group ML Research Phone, with worked solutions. A free account saves your progress.
What the ML Research Phone tests
Doubly-stochastic matrices, small-sample binomial median test, maybe one numpy coding task.
QuantVault maps 23 practice problems to this round. By topic, the biggest groups are regression (7), probability (4), linear algebra (3), optimization (3); by difficulty, 3 easy, 18 medium and 2 hard. 19 of them were reported by candidates who interviewed at The Voleon Group, most recently in Nov 2025.
- About an hour with a PhD researcher: linear algebra, OLS, regression slopes and probability puzzles.
- Say your plan before you compute; interviewers rarely redirect you, and they want the right answer, not only a good process.
Who takes this round: ML Research Staff candidates. See the full The Voleon Group process and who takes each round.
How to prepare for the ML Research Phone
- Derive OLS and logistic regression from scratch (closed form + gradient descent + optimal learning rate via the Hessian).
- The regression-range puzzles recur: R² combining bounds and the product of Y~X and X~Y slopes (∈ [0,1]).
- E[X | X+Y] for joint normals and doubly-stochastic-matrix facts are high-frequency.
Further reading: How quant superdays work · Behavioral questions at trading firms · Market-making game interview guide.
Question types in this round
The 5 largest question types in the The Voleon Group ML Research Phone practice set; across them the most common sub-topics are matrix operations, correlation, convex optimization, eigenvalues, expected value, numerical methods. The questions themselves, with worked solutions, are in the round practice.
Regression7 in this round
Probability4 in this round
Linear Algebra3 in this round
Optimization3 in this round
Expectation2 in this round
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Frequently asked questions
What is the The Voleon Group ML Research Phone interview?
It is stage 4 of 7 in the The Voleon Group interview process, after the Onsite / VO. Format: ~60 min · stats + ML. Stats + ML phone after a reading list (~10 intro, 40 tech, 10 Q&A): OLS closed form, when (XᵀX)⁻¹ exists, gradient-descent least squares in basic numpy, R²-combining, Y~X vs X~Y slope puzzles, E[X|X+Y] for joint normals. Doubly-stochastic matrices, small-sample binomial median test, maybe one numpy coding task.
How long is the The Voleon Group ML Research Phone interview?
Candidates report: ~60 min · stats + ML.
What questions come up in the The Voleon Group ML Research Phone interview?
The practice set QuantVault maps to this round centers on regression, probability, linear algebra.
How should I prepare for the The Voleon Group ML Research Phone interview?
Derive OLS and logistic regression from scratch (closed form + gradient descent + optimal learning rate via the Hessian). The regression-range puzzles recur: R² combining bounds and the product of Y~X and X~Y slopes (∈ [0,1]).
What comes after the ML Research Phone?
The Research VO + Deep-Dive (stage 5 of 7). Format: 2 × 2 hr · stats / ML / coding / research.
Practice the The Voleon Group ML Research Phone round
Work the 23 mapped practice problems with progress tracking, then move to the next stage of the The Voleon Group funnel.