Diagnose rising account switching and falling actives

Q: Diagnose rising account switching and falling actives

This question evaluates a data scientist's competency in diagnostic analytics, experiment diffing, cohort and identity-resolution analysis, metric instrumentation, and SQL-based quantitative validation.

Q: How do I approach Analytics & Experimentation interview questions?

Analytics & Experimentation questions require understanding of core concepts and practice. PracHub provides solutions with explanations to help you master analytics & experimentation interviews.

Q: What difficulty level is this interview question?

This is a hard difficulty Analytics & Experimentation question, commonly asked during Technical Screen rounds at Meta.

Q: What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Meta during technical interviews.

Question

Diagnostic Plan: Account Switching Up, Active Users Down

Context

You observed a sudden pattern: the number of users switching accounts increased, while overall active users decreased. Assume:

Active user = distinct user_id with any qualifying activity in a day (DAU) unless otherwise noted.
person_id is a cross-account identity (e.g., same human across multiple user_ids via SSO/identity graph).
An "account switch" is an explicit event (e.g., switch_account, add_account) or inferred by consecutive session logins to different user_ids from the same device/session.

Provide a concrete diagnostic plan covering (a)–(f).

Requirements

(a) List 5–7 plausible hypotheses spanning measurement artifacts, product changes, and behavior shifts.

(b) Specify the exact metrics and breakdowns you will pull (e.g., by client, geo, new vs returning, person_id vs user_id, cohorts, time-of-day).

(c) Describe at least three targeted slice analyses to confirm or refute cross-contamination between accounts (i.e., multiple accounts used by the same person/device).

(d) Outline event/experiment diffing steps to identify recent launches correlated with the shift.

(e) Provide minimal SQL or pseudocode to quantify how many active user_ids map to the same person_id compared with last week.

(f) List immediate mitigations if the root cause is: (i) a logging bug, (ii) authentication friction, or (iii) users gaming policy limits by rotating accounts.

Diagnose rising account switching and falling actives

Quick Overview

Diagnostic Plan: Account Switching Up, Active Users Down

Context

Requirements

Solution

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