Who's the Guinea Pig?: Investigating Online A/B/n Tests in-the-Wild

A/B/n testing has been adopted by many technology companies as a data-driven approach to product design and optimization. These tests are often run on their websites without explicit consent from users. In this paper, we investigate such online A/B/n tests by using Optimizely as a lens. First, we provide measurement results of 575 websites that use Optimizely drawn from the Alexa Top-1M, and analyze the distributions of their audiences and experiments. Then, we use three case studies to discuss potential ethical pitfalls of such experiments, including involvement of political content, price discrimination, and advertising campaigns. We conclude with a suggestion for greater awareness of ethical concerns inherent in human experimentation and a call for increased transparency among A/B/n test operators.