Time Series studies refer to the surveys ANES conducts during most years of national elections (since 2004, only during presidential elections). These studies consist of a pre- and post-election interview. Topics cover voting behavior and the elections, together with questions on public opinion and attitudes. Pilot studies test content and methodology for forthcoming Time Series studies. Pilot studies have been conducted ‘between’ most of the Time Series studies since 1979. Special studies is an umbrella term that includes studies that don’t fall into either of the other categories. These include panel studies (where respondents from a previous study have been re-interviewed over time), collaborative studies (e.g. ANES-GSS 2020 Joint Study), and other non-standard studies.