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Tesla·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

Tesla SWE interview that was heavier on stats than I expected. One question, but it had a lot of layers and I wasn't fully prepared for the multiple comparisons piece.

Questions Asked (1)

Q1

You have historical quality data for batteries randomly assigned to one of 5 groups. Each battery goes through 3 binary (pass/fail) quality tests. How would you determine which group has the best overall quality in a statistically rigorous way? Cover how you'd define a combined quality metric, handle unequal group sizes, quantify uncertainty, and deal with the multiple comparison problem.

A/B Testing & ExperimentationProduct Analytics & MetricsTechnical Trade-offs
Author's notes

I started with the composite metric part and that went okay.

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AI HintsAI Generated

Suggested Approach

Start by defining a combined quality metric that appropriately weights the three binary tests, then model the probability of passing all tests using logistic regression or a similar framework. Use Bayesian inference or bootstrapping to quantify uncertainty and apply multiple comparison corrections to identify the best group rigorously.

Pro tip: Emphasize that the choice of metric should align with business impact—e.g., if one test is more critical, weight it higher—and always validate assumptions with sensitivity analyses.

1. Define a Combined Quality Metric

Decide on a metric that aggregates the three binary tests, such as the probability of passing all tests (intersection) or a weighted sum of passes. Consider using a latent variable model (e.g., item response theory) to account for test difficulty and correlation.

2. Model Group Differences

Use logistic regression with group as a categorical predictor to estimate each group's probability of passing each test, or model the combined metric directly. For unequal group sizes, ensure the model accounts for varying sample sizes via weighting or Bayesian methods.

3. Quantify Uncertainty

Obtain confidence intervals or posterior distributions for each group's metric using bootstrapping or Bayesian credible intervals. This provides a range of plausible values and accounts for sampling variability.

4. Adjust for Multiple Comparisons

Apply a correction like Bonferroni, Holm-Bonferroni, or false discovery rate (FDR) to control the family-wise error rate when comparing all groups. Alternatively, use a Bayesian approach with informative priors or model-based comparisons.

5. Identify the Best Group

Rank groups by their estimated metric and determine if the top group is statistically significantly better than the others after adjustment. Consider practical significance and effect sizes, not just p-values.

Key Points to Mention

  • Choice of combined metric: probability of passing all tests vs. weighted sum, and its alignment with business goals.
  • Handling unequal group sizes: use of weighted regression, Bayesian models, or bootstrapping to avoid bias.
  • Uncertainty quantification: confidence intervals, credible intervals, or bootstrapped distributions.
  • Multiple comparison correction: Bonferroni, Holm, FDR, or Bayesian alternatives.
  • Model assumptions: independence of tests, correlation between tests, and potential interactions.
  • Practical significance: effect size and business impact, not just statistical significance.

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