The analysis of changes in party identification over time is based on a compilation of 266 telephone surveys and more than 360,000 interviews among registered voters conducted by Pew Research Center from January 1994 to September 2019. These surveys are combined into one large data file that can be sorted according to a range of demographic characteristics, with comparisons made across different time periods. Yearly totals are calculated by combining all surveys for the calendar year, with appropriate weights applied. Because fewer telephone polls were conducted in 2018 and 2019, data for those years has been combined in Chapter 1. The table below shows the number of surveys and interviews conducted each year as well as the margin of error for each yearly sample.

© Pew Research Center, 2020