Estimate billboard reach and impressions

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Quick Overview

This question evaluates probabilistic modeling and statistical inference skills applied to audience measurement and attribution, covering Poisson-based frequency modeling, visibility-adjusted impressions, panel-based deduplication and expansion, uncertainty propagation (delta method/bootstrap), and Markov-chain attribution within the Statistics & Math / Data Science domain. It is commonly asked to test the ability to convert traffic and visibility inputs into quantitative reach and impressions with propagated confidence intervals, reason about attribution via a 3-state Markov chain, identify measurement biases, and demonstrates both conceptual understanding and practical application through numerical estimation and sensitivity analysis.

Estimate billboard reach and impressions

Company: Pinterest

Role: Data Scientist

Category: Statistics & Math

Difficulty: hard

Interview Round: Onsite

A single digital billboard sits beside a 6-lane urban expressway. You must estimate weekly unique reach (people who saw it at least once) and total impressions, and then extend to estimate conversion to store visits using a simple Markov chain model. Given data and assumptions: - Average weekday vehicles/day: 80,000; weekend: 50,000. Average occupants/vehicle: 1.4. - Visibility probability per pass depends on lane and time: p_vis = 0.75 (daytime), 0.55 (night), weighted by 70% daytime traffic. - Share of traffic by segment: locals living within 3 km (30%), commuters passing ≥4 weekdays (50%), occasional passers (20%). - For commuters, passes/week ~ Poisson(λ=5). For locals, passes/week ~ Poisson(λ=2). For occasional, passes/week ~ Poisson(λ=1). - Deduplicate unique people using mobile location panel of 120,000 devices/week within 500 m; device-to-person expansion factor: 2.2; panel capture rate uncertainty ±10% (1σ). Tasks: 1) Estimate weekly unique reach and total impressions with 95% CIs, clearly stating all formulas and independence assumptions. Show how you combine traffic counts, occupancy, visibility, and pass frequency to compute impressions, and how you deduplicate to people-level using the panel (include the capture-rate uncertainty via delta method or bootstrap). 2) Using a 3-state Markov chain (Unaware → Aware → Visit), propose reasonable transition probabilities by segment and compute expected visits/week attributable to the billboard. Discuss sensitivity of results to these probabilities and to p_vis. 3) Identify at least three major bias sources (e.g., panel selection, deduplication error, dwell-time bias) and propose corrections/validations.

Overview: This question evaluates probabilistic modeling and statistical inference skills applied to audience measurement and attribution, covering Poisson-based frequency modeling, visibility-adjusted impressions, panel-based deduplication and expansion, uncertainty propagation (delta method/bootstrap), and Markov-chain attribution within the Statistics & Math / Data Science domain. It is commonly asked to test the ability to convert traffic and visibility inputs into quantitative reach and impressions with propagated confidence intervals, reason about attribution via a 3-state Markov chain, identify measurement biases, and demonstrates both conceptual understanding and practical application through numerical estimation and sensitivity analysis.

Read the full Pinterest Data Scientist interview experience this question came from

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Oct 13, 2025
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Digital Billboard: Weekly Reach, Impressions, and Store-Visit Attribution

Context

You are estimating the performance of a single digital billboard beside a 6‑lane urban expressway over one week. You must report weekly unique reach (people who saw it at least once) and total impressions, then attribute store visits via a simple 3‑state Markov chain. Assume traffic counts refer to passes that could potentially see the billboard (directionality already accounted for), and average vehicle occupancy applies uniformly.

Given Data and Assumptions

  • Traffic counts
    • Weekday vehicles/day: 80,000 (Mon–Fri)
    • Weekend vehicles/day: 50,000 (Sat–Sun)
    • Average occupants per vehicle: 1.4
  • Visibility probability per pass
    • Daytime p_vis_day = 0.75; Night p_vis_night = 0.55
    • Daytime traffic share = 70% (thus weekly average p_vis = 0.7×0.75 + 0.3×0.55)
  • Audience segments (share of traffic by passes)
    • Commuters (≥4 weekdays): 50%
    • Locals (within 3 km): 30%
    • Occasional passers: 20%
  • Pass frequency per person by segment (weekly)
    • Commuters: Poisson(λ=5)
    • Locals: Poisson(λ=2)
    • Occasional: Poisson(λ=1)
  • Panel for deduplication
    • Weekly unique devices within 500 m: 120,000
    • Device-to-person expansion factor: 2.2
    • Panel capture-rate uncertainty: ±10% (1σ), to be propagated (delta method or bootstrap)

Tasks

  1. Estimate weekly unique reach and total impressions with 95% confidence intervals. Clearly state all formulas and independence assumptions. Show how to combine traffic counts, occupancy, visibility, and pass frequency to compute impressions, and how to deduplicate to people-level using the panel (including the capture-rate uncertainty via delta method or bootstrap).
  2. Using a 3-state Markov chain (Unaware → Aware → Visit), propose reasonable segment-specific transition probabilities and compute expected visits/week attributable to the billboard. Discuss sensitivity to these probabilities and to p_vis.
  3. Identify at least three major sources of bias (e.g., panel selection, deduplication error, dwell-time bias) and propose corrections/validations.
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