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Lyft·Data Scientist·Technical Phone Screen·Senior

SeniorPrefer not to say
Jun 2026Remote

Summary

Lyft data scientist interview focused entirely on a two-part metric investigation case: a 7% drop in monthly active riders and a 20% spike in average wait time, both in the same month. The case was more layered than I expected and the follow-ups pushed hard on causality and experiment design.

Questions Asked (7)

Q1

Monthly Active Riders dropped 7% month over month. Walk me through how you would investigate this from start to finish.

Product Analytics & MetricsRoot Cause Analysis
Author's notes

My instinct was to jump straight into segmentation by metro and cohort, but I caught myself and backed up to data validation first.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the metric definition and validating the data to rule out tracking or pipeline issues. Then segment the drop by dimensions like geography, platform, rider type, and time to localize the cause, and finally test hypotheses around internal changes and external events to identify the root cause.

Pro tip: Always quantify the impact of each potential cause and prioritize by magnitude—this shows you can separate signal from noise and focus on what actually moves the metric.

1. Clarify and Validate the Metric

Confirm the exact definition of Monthly Active Riders (e.g., unique riders who took at least one ride in a month) and check data pipelines for errors, logging issues, or seasonality adjustments.

2. Segment the Drop

Break down the 7% decline by dimensions such as city, platform (iOS/Android), rider tenure (new vs. existing), ride type, and time (daily/weekly trends) to isolate where the drop is concentrated.

3. Generate Hypotheses

Brainstorm potential causes: internal factors (app bugs, pricing changes, marketing campaigns, product updates) and external factors (competitor launches, weather, holidays, economic shifts).

4. Test Hypotheses with Data

Use statistical tests, cohort analysis, and funnel analysis to validate or reject each hypothesis, and quantify the contribution of each factor to the overall drop.

5. Synthesize and Recommend

Summarize findings, identify the most likely root cause(s), and propose actionable next steps or further investigations to mitigate the decline.

Key Points to Mention

  • Metric definition and data validation to rule out false alarms
  • Segmentation by geography, platform, rider type, and time
  • Internal vs. external factors (e.g., app releases, competitor actions)
  • Quantifying impact of each factor to prioritize root causes
  • Cohort analysis to distinguish new vs. existing rider behavior
  • Actionable recommendations and monitoring plan

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

Q2

Average ride wait time went up 20% in the same month. How do you investigate that?

Root Cause AnalysisProduct Analytics & Metrics
Author's notes

Went straight to supply vs demand decomposition, which felt right.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the metric definition and the scope of the increase (e.g., all cities, specific hours, or rider segments), then systematically rule out data quality issues before diving into product, supply, and demand drivers. Use a structured root cause analysis to isolate the most likely causes and quantify their impact.

Pro tip: Always validate the data pipeline first—many 'metric changes' are actually logging or ETL errors. Also, consider external factors like weather or events that could affect both supply and demand simultaneously.

1. Clarify the metric and scope

Confirm how 'average ride wait time' is defined (e.g., time from request to pickup) and the exact time period. Break down the 20% increase by dimensions like city, hour of day, rider cohort, and ride type to localize the problem.

2. Check data quality and instrumentation

Investigate whether the increase is real or due to data issues: logging errors, changes in event tracking, pipeline delays, or metric definition changes. Compare with other related metrics (e.g., ride requests, cancellations) for consistency.

3. Analyze supply-side factors

Examine driver supply: number of active drivers, driver hours, driver acceptance rates, and driver positioning. Look for changes in driver incentives, onboarding, or churn that could reduce supply and increase wait times.

4. Analyze demand-side and external factors

Check demand patterns: ride request volume, surge pricing, and rider behavior. Consider external events (weather, holidays, concerts) or competitor actions that could spike demand or reduce supply.

5. Synthesize findings and quantify impact

Correlate the timing of the increase with potential causes, perform statistical tests or causal inference if possible, and estimate the contribution of each factor. Recommend next steps for mitigation or further investigation.

Key Points to Mention

  • Segment the metric by geography, time, and user/driver cohorts to identify where the increase is concentrated.
  • Rule out data pipeline issues, logging changes, or metric definition shifts before assuming a real change.
  • Consider supply-side metrics: driver availability, acceptance rates, and incentives.
  • Consider demand-side metrics: ride request volume, surge pricing, and external events.
  • Check for seasonality or one-off events (e.g., weather, holidays) that could explain the spike.
  • Use statistical methods (e.g., hypothesis testing, causal inference) to validate hypotheses and quantify impact.

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

Q3

Before assuming either metric movement is real, what would you check first?

Product Analytics & MetricsRoot Cause Analysis
Author's notes

Data quality stuff: instrumentation changes, app version rollouts that might affect event logging, late-arriving data, bot or duplicate filtering.

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AI HintsAI Generated

Suggested Approach

Start by acknowledging that any metric movement could be due to data quality issues, instrumentation changes, or external factors before concluding it's a real product change. Then outline a systematic validation process: check data pipeline health, logging, and experiment setup, then segment and compare with other metrics to confirm the movement's validity.

Pro tip: Always validate the data first—many 'insights' are just broken dashboards or logging bugs. Mention that you'd check if the movement aligns with known events (e.g., holidays, outages) and if it's consistent across independent data sources.

1. Verify Data Quality and Pipeline Health

Check for data freshness, completeness, and anomalies in ETL jobs. Ensure no upstream data issues, schema changes, or missing data that could cause spurious movement.

2. Validate Instrumentation and Logging

Confirm that event tracking, logging, and metric definitions haven't changed recently. Look for deployments or configuration changes that might alter how data is captured.

3. Check for External Factors and Seasonality

Consider holidays, marketing campaigns, competitor actions, or platform outages that could explain the movement. Compare with historical patterns and seasonality.

4. Segment and Cross-Validate

Break down the metric by dimensions (e.g., geography, user type, device) to see if the movement is broad or isolated. Cross-check with other related metrics to see if they move in expected directions.

5. Assess Statistical Significance and Experiment Design

If from an A/B test, check for sample ratio mismatch, novelty effects, or peeking. Ensure the movement is statistically significant and not due to random noise.

Key Points to Mention

  • Data pipeline health: freshness, completeness, and anomalies
  • Instrumentation changes: logging, event tracking, metric definitions
  • External factors: seasonality, holidays, marketing, outages
  • Segmentation: breakdown by dimensions to isolate the movement
  • Cross-validation: compare with other metrics and data sources
  • Statistical significance: sample size, p-value, confidence intervals, and experiment validity

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

Q4

If the entire MAR drop turns out to be concentrated in one large metro, how does that change your conclusion and your recommendation?

Root Cause AnalysisProduct Strategy
Author's notes

This one actually tripped me up a little.

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AI HintsAI Generated

Suggested Approach

First, acknowledge that geographic concentration changes the root cause hypothesis from a broad, systemic issue to a localized one, likely tied to market-specific factors. Then, propose a structured plan to validate the concentration, identify the unique drivers in that metro, and tailor recommendations accordingly, while considering whether the issue is truly isolated or a leading indicator for other markets.

Pro tip: Emphasize the importance of distinguishing between correlation and causation—just because the drop is concentrated doesn't mean the metro is the cause; it could be a symptom of a broader issue that manifests unevenly. Also, quantify the impact on overall metrics to prioritize action.

1. Validate the concentration

Confirm that the MAR drop is indeed concentrated in one metro by analyzing the data at a granular level (e.g., by city, zone, or rider cohort) and checking for statistical significance. Ensure the concentration isn't an artifact of data aggregation or seasonality.

2. Identify potential metro-specific drivers

Investigate factors unique to that metro, such as local competition, regulatory changes, pricing changes, marketing campaigns, supply issues (driver availability), or external events (e.g., weather, transit strikes). Compare with other metros to isolate what's different.

3. Assess broader implications

Determine if the metro-specific issue could spread to other markets or if it's truly isolated. Consider whether the metro is a bellwether for trends that might affect other regions, and evaluate the overall impact on company-wide MAR.

4. Refine root cause hypothesis

Based on the drivers identified, update your root cause analysis: Is it a local operational problem, a strategic misstep, or an external shock? Use data to test hypotheses and quantify the contribution of each factor to the drop.

5. Tailor recommendations

Develop targeted recommendations for that metro (e.g., local marketing, driver incentives, pricing adjustments) while also considering whether to replicate successful strategies elsewhere or implement company-wide changes if the issue is symptomatic of a larger problem.

Key Points to Mention

  • Geographic segmentation and drill-down analysis to confirm concentration
  • Local market dynamics: competition, regulations, supply/demand imbalances
  • Comparison with other metros to identify unique factors
  • Quantification of the metro's contribution to overall MAR drop
  • Potential for spillover effects or leading indicators
  • Targeted vs. broad interventions and ROI of recommendations

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

Q5

Could the wait time increase be causing part of the MAR decline? How would you test for that causal link and try to quantify it?

A/B Testing & ExperimentationRoot Cause AnalysisProduct Analytics & Metrics
Author's notes

This was the most interesting follow-up.

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AI HintsAI Generated

Suggested Approach

First, clarify the metrics and the hypothesized causal pathway: wait time increase → rider/driver behavior changes → MAR decline. Then propose a mix of observational (e.g., regression with controls, instrumental variables) and experimental (e.g., A/B test manipulating wait time) methods to test causality and quantify the effect size.

Pro tip: Emphasize that correlation isn't causation and that you'd triangulate with multiple methods (e.g., natural experiments, switchback tests) to rule out confounders like seasonality or supply shocks. Also, quantify the impact in business terms (e.g., incremental MAR loss per minute of wait time) to make it actionable.

1. Clarify definitions and mechanism

Define MAR and wait time precisely (e.g., MAR = matched acceptance rate? or monthly active riders?; wait time = pickup ETA). Map the hypothesized causal chain: increased wait time → lower rider satisfaction → fewer rides → MAR decline.

2. Check for correlation and confounders

Plot time series of wait time and MAR, compute correlation, and identify potential confounders (e.g., seasonality, competitor promotions, supply changes). Use regression with controls to see if the relationship holds.

3. Design causal tests

Propose experimental designs: A/B test where wait time is artificially manipulated (e.g., by adjusting dispatch radius), or natural experiments (e.g., policy change, weather shock). Use difference-in-differences or instrumental variables if randomization isn't feasible.

4. Quantify the effect

Estimate the causal effect size (e.g., a 1-minute increase in wait time causes X% decline in MAR). Use regression discontinuity, propensity score matching, or causal forests to quantify heterogeneous effects.

5. Validate and iterate

Check robustness (e.g., placebo tests, sensitivity analysis) and consider alternative explanations. If effect is significant, recommend mitigation strategies (e.g., reduce wait time) and measure impact.

Key Points to Mention

  • Define MAR and wait time clearly; ensure alignment with business context (e.g., MAR could be 'Monthly Active Riders' or 'Match Acceptance Rate').
  • Use causal inference methods: randomized experiments (A/B tests), quasi-experimental designs (DiD, IV), and observational causal models (propensity scores, causal forests).
  • Control for confounders: time trends, seasonality, supply/demand shocks, competitor actions, and user composition changes.
  • Quantify effect size with confidence intervals and business impact (e.g., 'each additional minute of wait time reduces MAR by 0.5%').
  • Consider heterogeneous effects: impact may vary by rider segment, geography, or time of day.
  • Acknowledge limitations: experiments may be costly or unethical; observational methods rely on assumptions (e.g., unconfoundedness).

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

Q6

A pricing change shipped mid-month in only half the metros. How would you use that rollout to estimate its causal effect on both metrics?

A/B Testing & ExperimentationRoot Cause Analysis
Author's notes

Natural experiment setup.

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AI HintsAI Generated

Suggested Approach

Treat the partial rollout as a natural experiment and use a difference-in-differences (DiD) design comparing treated vs. control metros before and after the change. Verify parallel pre-trends, then estimate the causal effect on each metric separately, accounting for metro-level clustering and potential spillovers.

Pro tip: Proactively discuss threats to validity like spillovers, anticipation effects, and heterogeneous treatment timing, and suggest robustness checks such as synthetic control or event-study plots to strengthen your causal claim.

1. Define treatment and control groups

Identify which metros received the pricing change (treated) and which did not (control), ensuring they are comparable on pre-period characteristics and not subject to other simultaneous interventions.

2. Validate parallel trends assumption

Plot pre-treatment trends for each metric in treated vs. control metros and run placebo tests or event-study regressions to confirm the groups moved similarly before the change.

3. Estimate causal effect with DiD

Fit a difference-in-differences model (e.g., two-way fixed effects) for each metric, clustering standard errors at the metro level, and interpret the interaction term as the causal effect.

4. Check robustness and heterogeneity

Conduct sensitivity analyses: vary control group, use synthetic control or matching, test for spillovers, and examine effect heterogeneity across metro characteristics.

5. Communicate results and limitations

Present effect sizes with confidence intervals, discuss practical significance, and clearly state assumptions and limitations of the quasi-experimental design.

Key Points to Mention

  • Difference-in-differences (DiD) design and its assumptions
  • Parallel trends assumption and pre-trend validation
  • Clustering standard errors at the metro level
  • Potential spillover effects between treated and control metros
  • Heterogeneous treatment effects across metros
  • Robustness checks like synthetic control or event-study analysis

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

Q7

After shipping a fix, how do you confirm the metric actually recovered because of your fix and not just natural reversion to the mean?

A/B Testing & ExperimentationAdaptability & Ambiguity
Author's notes

Honestly the question I felt least prepared for.

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AI HintsAI Generated

Suggested Approach

Start by acknowledging the challenge of causal inference in observational settings, then outline a structured approach that combines pre/post analysis with control groups and statistical methods to isolate the fix's impact. Emphasize the importance of defining a clear counterfactual and using techniques like difference-in-differences, synthetic controls, or interrupted time series to account for natural reversion. Conclude by discussing how you would validate assumptions and communicate uncertainty to stakeholders.

Pro tip: Proactively mention that you would pre-register your analysis plan and check for pre-existing trends to avoid p-hacking and ensure robustness. Also, consider running a holdback experiment if feasible, as it provides the strongest causal evidence.

1. Define the counterfactual

Clearly articulate what would have happened without the fix. Identify a suitable control group (e.g., similar regions, users, or time periods) or use a holdback group if available.

2. Check pre-intervention trends

Analyze the metric before the fix to ensure the treatment and control groups were on parallel trends. If not, adjust using methods like difference-in-differences or synthetic control.

3. Apply causal inference methods

Use techniques such as difference-in-differences, interrupted time series, or synthetic control to estimate the fix's effect while controlling for natural reversion and other confounders.

4. Validate with robustness checks

Test the sensitivity of your results to different model specifications, placebo tests, and alternative control groups. Check if the effect size is consistent across subgroups.

5. Communicate uncertainty and next steps

Present the estimated effect with confidence intervals, discuss limitations, and recommend further validation (e.g., a holdback experiment) if needed.

Key Points to Mention

  • Difference-in-differences (DiD) and its assumptions (parallel trends)
  • Synthetic control method for constructing a counterfactual
  • Interrupted time series analysis to account for seasonality and trends
  • Placebo tests and robustness checks to rule out spurious correlations
  • The importance of pre-registration and avoiding p-hacking
  • When possible, running a holdback experiment for stronger causal inference

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