Design experiment for ads in chat with budgets

## Context After launching an AI chat feature, the company wants to show **ads inside the chat experience** (you are interviewing for an Ads/Monetization data science role). Advertisers have **fixed budgets**, so shifting impressions to chat may reallocate spend from other placements. ## Task Design an experiment to measure the incremental impact of introducing chat ads. ### Requirements 1. Define the main **incrementality question** (platform revenue vs advertiser outcomes vs user experience). 2. Propose an A/B (or alternative) design that addresses: - budget constraints / budget reallocation (“budget split”) - auction dynamics and supply shift - user-level effects and advertiser-level effects 3. Specify **primary, diagnostic, and guardrail metrics**. 4. Describe how you would interpret results under different scenarios (e.g., revenue up but ROAS down).