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Snapchat·Data Scientist·Technical Phone Screen·Intermediate

IntermediatePrefer not to say
Apr 2026Remote

Summary

Snapchat data scientist interview that leaned heavily on probability fundamentals. The Bayes' theorem question was the centerpiece and required a full worked example from scratch, not just a formula recitation.

Questions Asked (1)

Q1

Walk through a complete Bayes' theorem calculation using a concrete example. Define your prior and likelihoods, write out the full formula, then compute the posterior and give a final numeric answer.

Product Analytics & MetricsAlgorithms & Data Structures
Author's notes

I went with the classic disease-test setup because it's easy to plug numbers into, but I fumbled the denominator for a bit.

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AI HintsAI Generated

Suggested Approach

Choose a concrete, relatable example—ideally from Snapchat's domain like ad click-through or spam detection—and clearly define the prior and likelihoods before plugging into Bayes' theorem. Walk through the arithmetic step-by-step, narrating each component, and end with a clear numeric posterior and its practical interpretation.

Pro tip: Use a Snapchat-relevant example (e.g., detecting spam accounts or predicting ad engagement) to show product sense, and sanity-check your result by comparing it to the base rate—this demonstrates statistical maturity.

1. Choose a concrete example

Select a simple, realistic scenario relevant to Snapchat, such as whether a user will tap on an ad given their past behavior. State the event of interest and the available evidence.

2. Define prior and likelihoods

Clearly assign numeric values to the prior probability P(H) and the conditional probabilities P(E|H) and P(E|¬H). Explain what each represents in your example.

3. Write the full formula

State Bayes' theorem: P(H|E) = [P(E|H) * P(H)] / [P(E|H)*P(H) + P(E|¬H)*P(¬H)]. Show the denominator as the total probability of the evidence.

4. Compute the posterior

Plug in the numbers and perform the arithmetic step-by-step, simplifying fractions or decimals as needed. Arrive at a numeric posterior probability.

5. Interpret and sanity-check

Explain what the posterior means in context (e.g., 'There is a 75% chance the user will tap the ad'). Compare it to the prior to show how the evidence updated the belief.

Key Points to Mention

  • Bayes' theorem formula and its components: prior, likelihood, evidence, posterior
  • The law of total probability for computing the denominator
  • Concrete numeric values for prior and likelihoods, with clear definitions
  • Step-by-step arithmetic to avoid calculation errors
  • Interpretation of the posterior in the context of the example
  • Sanity check: posterior should lie between 0 and 1 and reflect the strength of evidence

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