PracHub
QuestionsPremiumLearningGuidesInterview PrepNEWCoaches
|Home/Analytics & Experimentation/Reddit

Design a causal evaluation without A/B testing

Last updated: Mar 29, 2026

Quick Overview

This question evaluates a data scientist's competency in causal inference, time-series analysis, and synthetic control methodology for non-randomized experiments, including donor pool construction, pre/post diagnostics, and sensitivity and heterogeneity assessments.

  • hard
  • Reddit
  • Analytics & Experimentation
  • Data Scientist

Design a causal evaluation without A/B testing

Company: Reddit

Role: Data Scientist

Category: Analytics & Experimentation

Difficulty: hard

Interview Round: Technical Screen

A high-impact feature cannot be A/B tested due to policy/infra constraints, but leadership needs a go/no-go decision. Propose a complete analysis plan using Synthetic Control (or justify an alternative). Specify: (a) the treatment unit and donor pool construction, including eligibility/exclusion rules to prevent contamination or anticipation; (b) pre-intervention window length and how you’ll handle seasonality, holidays, macro shocks, and data latency; (c) primary outcome and guardrail metrics, with pre-registered success thresholds and a decision rubric; (d) which predictors to include (outcome lags vs. covariates), weight constraints, and how you’ll tune hyperparameters; (e) diagnostics you will require before trusting effects (pre-period RMSPE targets, in-space and in-time placebo tests, pre/post fit plots), and your inference approach (MSPE ratio/permutation tests, uncertainty bands for pointwise and cumulative effects); (f) sensitivity analyses (leave-one-out donors, alternative windows, augmented/regularized SCM, donor reweighting) and how you’ll bound spillovers; (g) heterogeneity and persistence analyses (subgroups, dynamic effects); (h) what you will do if pre-period fit is poor or donors are scarce; and (i) how the results map to a staged launch, rollback criteria, and post-launch monitoring.

Quick Answer: This question evaluates a data scientist's competency in causal inference, time-series analysis, and synthetic control methodology for non-randomized experiments, including donor pool construction, pre/post diagnostics, and sensitivity and heterogeneity assessments.

Related Interview Questions

  • Measure impact of ads-manager automation feature - Reddit (easy)
  • Design experiment for ads in chat with budgets - Reddit (easy)
  • Design A/B test for AI chat box - Reddit (easy)
Reddit logo
Reddit
Oct 13, 2025, 9:49 PM
Data Scientist
Technical Screen
Analytics & Experimentation
1
0

Non-Randomized Launch Decision via Synthetic Control: Complete Analysis Plan

You need to make a go/no-go decision for a high-impact feature that cannot be A/B tested due to policy/infrastructure constraints. Assume we can gate the feature to one or a small number of units (e.g., a geography × platform cell) and measure time-series KPIs across comparable units.

Propose a complete analysis plan using Synthetic Control (or justify an alternative if SCM is unsuitable). Address the following:

(a) Treatment unit and donor pool construction

  • Define the treatment unit precisely.
  • Specify how you will build the donor pool.
  • Eligibility/exclusion rules to prevent contamination, spillovers, and anticipation effects.

(b) Pre-intervention window and external factors

  • Pre-period length and rationale.
  • How you will handle seasonality, holidays, macro shocks, and data latency/backfill.

(c) Metrics and decision rubric

  • Primary outcome and guardrail metrics.
  • Pre-registered success thresholds and a clear go/no-go decision rule.

(d) Predictors, weights, and tuning

  • Which predictors to include (outcome lags vs. covariates).
  • Weight constraints and how you will tune hyperparameters.

(e) Diagnostics and inference

  • Required diagnostics before trusting effects (e.g., pre-period RMSPE targets, placebo tests in-space/in-time, pre/post fit plots).
  • Inference approach (MSPE ratio/permutation tests, uncertainty bands for pointwise and cumulative effects).

(f) Sensitivity and spillovers

  • Sensitivity analyses (leave-one-out donors, alternative windows, augmented/regularized SCM, donor reweighting).
  • How you will bound and assess spillovers/contamination.

(g) Heterogeneity and persistence

  • Subgroup and dynamic-effect analyses to assess heterogeneity and persistence/decay.

(h) Fallbacks

  • What you will do if pre-period fit is poor or donors are scarce.

(i) Launch mapping

  • How results translate into a staged launch plan, rollback criteria, and post-launch monitoring.

Solution

Show

Comments (0)

Sign in to leave a comment

Loading comments...

Browse More Questions

More Analytics & Experimentation•More Reddit•More Data Scientist•Reddit Data Scientist•Reddit Analytics & Experimentation•Data Scientist Analytics & Experimentation
PracHub

Master your tech interviews with 7,500+ real questions from top companies.

Product

  • Questions
  • Learning Tracks
  • Interview Guides
  • Resources
  • Premium
  • For Universities
  • Student Access

Browse

  • By Company
  • By Role
  • By Category
  • Topic Hubs
  • SQL Questions
  • Compare Platforms
  • Discord Community

Support

  • support@prachub.com
  • (916) 541-4762

Legal

  • Privacy Policy
  • Terms of Service
  • About Us

© 2026 PracHub. All rights reserved.