Gallup: Forty-two percent of Americans, on average, identified as political independents in 2013, the highest Gallup has measured since it began conducting interviews by telephone 25 years ago. Meanwhile, Republican identification fell to 25%, the lowest over that time span. At 31%, Democratic identification is unchanged from the last four years but down from 36% in 2008.

The results are based on more than 18,000 interviews with Americans from 13 separate Gallup multiple-day polls conducted in 2013.

In each of the last three years, at least 40% of Americans have identified as independents. These are also the only years in Gallup’s records that the percentage of independents has reached that level.

Americans’ increasing shift to independent status has come more at the expense of the Republican Party than the Democratic Party. Republican identification peaked at 34% in 2004, the year George W. Bush won a second term in office. Since then, it has fallen nine percentage points, with most of that decline coming during Bush’s troubled second term. When he left office, Republican identification was down to 28%. It has declined or stagnated since then, improving only slightly to 29% in 2010, the year Republicans “shellacked” Democrats in the midterm elections.

Not since 1983, when Gallup was still conducting interviews face to face, has a lower percentage of Americans, 24%, identified as Republicans than is the case now. That year, President Ronald Reagan remained unpopular as the economy struggled to emerge from recession. By the following year, amid an improving economy and re-election for the increasingly popular incumbent president, Republican identification jumped to 30%, a level generally maintained until 2007.

Democratic identification has also declined in recent years, falling five points from its recent high of 36% in 2008, the year President Barack Obama was elected. The current 31% of Americans identifying as Democrats matches the lowest annual average in the last 25 years.