Design a switchback and choose block length
Company: Uber
Role: Data Scientist
Category: Analytics & Experimentation
Difficulty: hard
Interview Round: Technical Screen
Design a switchback experiment for airport pickup pricing in a marketplace with spillovers. Choose the block length and rotation schedule using empirical autocorrelation and carryover: median trip duration = 22 minutes; demand ACF falls below 0.1 at 75 minutes; strong peaks every ~4 hours. Specify: (a) block length selection to minimize carryover yet retain power, (b) diagnostics to detect residual carryover (pre/post contrasts, lag terms), and (c) variance and sample-size computation under block randomization (include formulas and required inputs). Describe how you will randomize across time-of-day and days-of-week and how you will incorporate covariate adjustment (e.g., CUPED) to reduce variance.
Quick Answer: This question evaluates a candidate's competency in experimental design and causal inference for time-varying treatments, covering switchback experiments, handling spillovers and carryover, block randomization, variance and sample-size computation, temporal randomization (time-of-day and day-of-week), and covariate adjustment methods such as CUPED.