READ MOREAt least four in 10 Americans have been political independents in seven of the past eight years, including a record-high 43% in 2014.
The trend is based on aggregated data from all Gallup polls conducted in each year.
The 2018 aggregate includes 13 separate surveys, encompassing interviews with more than 13,000 U.S. adults. Gallup asks Americans in every poll it conducts whether they identify politically as a Democrat, a Republican or an independent.
Over the past 30 years, when Gallup has regularly conducted its surveys by telephone, independents have typically outnumbered Republicans and Democrats.
However, in just the past decade, an increasing proportion of adults have identified as independents, reaching 40% for the first time in 2011 and generally maintaining or exceeding that level since then.
As a result, since 2011, the percentage of independents has exceeded the percentage identifying with the Democratic Party by 11 points on average, and the percentage identifying as Republicans by 14 points.
The one recent year in which independent identification fell below 40% was 2016, when 39% of Americans did so.
The dip that year is consistent with the historical pattern by which fewer Americans identify as independents in presidential election years, when a flood of publicity for the two major parties tends to activate partisan leanings.
Since 1992, the percentage of independents has dropped three percentage points on average in presidential election years.
The recent rise in independent identification has come at the expense of both parties about equally. Compared with 30 years ago, when 33% of Americans identified as independents, the percentage of Republicans has fallen five points and the percentage of Democrats has fallen six points.
The proportion identifying with each party is near its low in the telephone-polling era. The 26% identifying as Republicans is one point above the low from 2013, and the 30% identifying as Democrats is one point above its 2015 and 2017 lows.
Gallup has asked the same party identification question it does today in polls as far back as 1951. Gallup interviewing in the 1950s through the mid-1980s mostly used a face-to-face mode rather than the telephone.
Experiments at the time suggested the results obtained by phone versus in-person interviewing differed slightly.
Even acknowledging those methodological differences, it is safe to conclude that the percentage of independents today is higher than in any year since at least 1951, given that many fewer identified as independents in the 1950s, 1960s, 1970s and 1980s than do so today.
Accordingly, the percentage of Democratic identifiers is near its historical lows, because the percentage of Democrats in the 1950s through 1980s was much higher than in any recent year.
Gallup did measure lower proportions of Republican identifiers after Watergate in the mid- to late 1970s, with percentages in the low 20s, so the current levels of Republican identification are probably not among the lowest Gallup has ever measured.
Americans' assessment of their political ideology was unchanged in 2018 compared with the year prior when 35% on average described themselves as conservative, 35% as moderate and 26% as liberal.
Although conservatives continue to outnumber liberals, the gap in conservatives' favor has narrowed from 19 percentage points in Gallup's 1992 baseline measurement to nine points each of the past two years. ■