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Lyft·Data Scientist·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Interviewed for a Data Scientist role at Lyft. One probability question that sounds straightforward until you realize you need to set up the conditional correctly.

Questions Asked (1)

Q1

A rider takes Lyft home. What's the probability they also took Lyft to work?

Product Analytics & Metrics
Author's notes

I knew this was a Bayes setup but fumbled the direction of conditioning for a second.

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AI HintsAI Generated

Suggested Approach

Clarify the question by defining the population and time frame, then use Bayes' theorem with conditional probabilities estimated from Lyft's data. Discuss how to derive P(took Lyft to work | took Lyft home) using trip history and user segmentation.

Pro tip: Show awareness of data limitations and propose a practical method to estimate the probabilities, such as using historical ride data or A/B testing, rather than just theoretical calculations.

1. Clarify the question

Define what 'took Lyft home' and 'took Lyft to work' mean, including time frames (e.g., same day, typical behavior) and population (e.g., all riders, commuters).

2. Identify relevant probabilities

Determine the conditional probability P(To Work | Home) and recognize that it can be computed using Bayes' theorem: P(To Work | Home) = P(Home | To Work) * P(To Work) / P(Home).

3. Estimate probabilities from data

Discuss how to estimate each component from Lyft's data: P(To Work) as the overall proportion of riders who take Lyft to work, P(Home) as the proportion who take Lyft home, and P(Home | To Work) as the likelihood of taking Lyft home given they took it to work.

4. Consider assumptions and biases

Address potential biases such as selection bias (only observing riders who use Lyft) and confounding factors (e.g., time of day, location, user habits).

5. Compute and interpret

Plug in estimated values to compute the probability, and interpret the result in business terms, noting any caveats about data quality and generalizability.

Key Points to Mention

  • Bayes' theorem and conditional probability
  • Definition of the population and time frame
  • Data sources: ride history, user profiles, commute patterns
  • Assumptions: independence, representativeness
  • Potential biases: selection bias, confounding variables
  • Business implications: understanding rider behavior for targeted promotions

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