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Prep plan
Updated weekly · Last refresh Aug 30

Lumen Data Scientist Interview Questions

The questions to prepare for a Lumen Data Scientist interview. Questions from real interview reports rank first. Updated weekly.

39questions
~6htotal time
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1
Statistics & ProbabilityStart here. 4 questions · ~34 min
Retention Change vs SeasonalityHard

Distinguish a true retention impact from seasonality using causal inference, time series controls, and pre-period adjustment.

Hypothesis TestingCausal InferenceTime SeriesLumen
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2
A/B Testing & Experimentation3 questions · ~26 min
Design Test for Novelty and SpilloversHard

Design an experiment that accounts for novelty effects and network spillovers before deciding whether to ship.

Network InterferenceExperimentationNovelty EffectLumen
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3
Machine Learning8 questions · ~68 min
Supervised vs Unsupervised LearningEasy

Explain how supervised and unsupervised learning differ, and ground the distinction in a practical ML example.

Unsupervised LearningFeature EngineeringBias-Variance TradeoffLumen
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4
Behavioral & Leadership15 questions · ~128 min
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5
More topics9 questions · ~77 min
Analyze Customer Purchase Trends with Window FunctionsEasy
Practice

Calculate the monthly spending trends for customers using window functions and joins.

Lumen
Debugging Production Data PipelinesMedium

A structured approach to debugging production data pipelines, with focus on orchestration, data quality, idempotency, and safe backfills.

InfrastructureToolsQualityLumen
Define Metrics for New FeaturesMedium

Define a success metric for a new feature that captures real user value, not just raw usage.

MetricsFeature Prioritizationuser valueLumen
Assess Analysis Accuracy and ReliabilityEasy

Explain how you validate that model evaluation results are accurate, reliable, and trustworthy before they are used.

Cross-ValidationCalibrationAccuracyLumen
Visualize Metrics to Show TrendsEasy

Choose visuals that make trend direction, comparisons, and KPI drivers easy to understand at a glance.

KPIsLeading IndicatorsDiagnosisLumen
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Hands-on SQL practiceWrite and run real queries in the editor. 2 drills · ~20 min
The finish line: interview-readyComplete all 39 questions plus 2 hands-on drills to finish this plan.