← DoorDash Interview Insights

DoorDash·Data Scientist·Technical Phone Screen·Senior

Senior
Jul 2026

Summary

DoorDash data science interview with a meaty marketplace diagnosis case that turned into a full experiment design problem. The scope was broader than I expected and the second half caught me pretty flat-footed.

Questions Asked (2)

Q1

Completed orders in the Los Angeles market dropped meaningfully. Walk through how you'd investigate this end to end.

Root Cause AnalysisProduct Analytics & Metrics
Author's notes

I started with the funnel breakdown which felt right, app sessions down to completed orders, but I kept second-guessing whether to lead with supply or demand.

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AI HintsAI Generated

Suggested Approach

Start by validating the metric definition and data pipeline to rule out instrumentation issues, then segment the drop by dimensions like time, geography, user type, and order characteristics to isolate the cause. Finally, correlate with external events and internal changes, and quantify the impact to prioritize next steps.

Pro tip: Always check if the drop is real before diving deep—many 'drops' are due to logging errors, dashboard bugs, or seasonality. Also, consider the broader business context: a drop in completed orders might be intentional (e.g., reducing fraud) or offset by other metrics.

1. Validate the metric and data quality

Confirm the drop is real by checking data pipelines, logging, and metric definitions. Ensure there are no instrumentation errors, missing data, or changes in how completed orders are counted.

2. Segment and localize the drop

Break down the metric by time (daily/weekly), geography (sub-markets, neighborhoods), user segments (new vs. existing, device), and order characteristics (restaurant type, delivery time) to identify where the drop is concentrated.

3. Generate and test hypotheses

Form hypotheses based on segments: supply issues (fewer Dashers, restaurant closures), demand issues (fewer users, lower conversion), operational issues (longer delivery times, cancellations), or external factors (weather, holidays, competitors).

4. Correlate with internal and external events

Check for recent product changes, marketing campaigns, pricing updates, or operational shifts. Also consider external events like weather, traffic, local regulations, or competitor actions.

5. Quantify impact and recommend actions

Estimate the contribution of each factor to the drop, prioritize based on impact and feasibility, and propose next steps such as deeper analysis, A/B tests, or operational fixes.

Key Points to Mention

  • Metric definition: Ensure 'completed orders' excludes cancellations, refunds, and failed deliveries consistently.
  • Segmentation: Analyze by time, geography, user cohorts, restaurant partners, and delivery logistics.
  • Supply-side factors: Dasher availability, restaurant capacity, and delivery times.
  • Demand-side factors: User acquisition, retention, conversion rates, and order frequency.
  • External factors: Weather, traffic, holidays, local events, and competitor promotions.
  • Internal changes: Product updates, pricing changes, marketing campaigns, and operational policies.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.

Q2

The investigation points to merchants being online fewer minutes per day. Design an experiment to test an incentive program meant to fix that.

A/B Testing & ExperimentationProduct Analytics & MetricsRoot Cause Analysis
Author's notes

This is where the interview got interesting and also where I started to feel the pressure.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the metric definition and the proposed incentive, then design a randomized controlled experiment with a clear hypothesis, primary metric (online minutes per day), guardrail metrics, and power analysis. Outline the rollout plan, analysis approach, and how you'll interpret results to decide whether to scale, iterate, or stop.

Pro tip: Define the metric precisely and consider whether the incentive could cause gaming or unintended consequences; always include guardrail metrics like order completion rate and merchant satisfaction to ensure the fix doesn't harm other parts of the business.

1. Clarify the problem and hypothesis

Confirm what 'online minutes per day' means (e.g., time logged into the merchant portal or app) and the proposed incentive. State a clear hypothesis: the incentive will increase online minutes per day for treated merchants.

2. Define metrics and experiment design

Choose the primary metric (average daily online minutes per merchant), secondary metrics (e.g., orders, revenue), and guardrails (e.g., cancellation rate, merchant satisfaction). Decide on randomization unit (merchant-level), sample size, and duration via power analysis.

3. Implement and run the experiment

Randomly assign merchants to treatment (incentive) and control (no incentive) groups. Ensure proper tracking and data collection, and monitor for any technical issues or novelty effects during the test period.

4. Analyze results and make a decision

Compare the primary metric between groups using appropriate statistical tests (e.g., t-test or regression with covariates). Check guardrails and segment analyses (e.g., by merchant size or region) to understand heterogeneity. Decide whether to scale, iterate, or stop based on statistical and practical significance.

Key Points to Mention

  • Randomization at the merchant level to avoid contamination and ensure valid comparison.
  • Power analysis to determine sample size and experiment duration, accounting for daily variability.
  • Primary metric: average online minutes per day per merchant; consider log transformation if skewed.
  • Guardrail metrics: order volume, cancellation rate, merchant satisfaction, and support tickets.
  • Potential novelty effect and the need for a sufficient washout period or long-term holdout.
  • Segmentation analysis to identify which merchant segments respond best to the incentive.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.