1. Note that the sample selection process requires identifying the specific country in which each user is located. This information was inferred from the “time zone” and “location” fields in the user profile, which was sufficient to identify the country of residence in 90% of the cases. This proportion is lower when we consider more specific geographical levels, such as state in the United States (71%).
2. A Bridge to Somewhere: Mapping State and Congressional Ideology on a Cross-institutional Common Space
3. See Section A of the supplementary materials for a summary of previous studies measuring ideology using social media.
4. Kwak H. , Lee C. , Park H. , and Moon S. 2010. What is Twitter, a social network or a news media? Proceedings of 19th International Conference on World Wide Web. ACM, 591–600.
5. Leapfrog Representation and Extremism: A Study of American Voters and Their Members in Congress