On Jan. 15, Pat Tiberi became the 12th member of the 115th Congress to resign from office. If that feels like a lot, that’s because it is; it’s the most people who have resigned from Congress through this point in the session in at least 117 years.

Since March 4, 1901 — the first day of the 57th Congress — 615 members of Congress have resigned or been removed from office. FiveThirtyEight canvassed them all, from Hazel Abel to Ryan Zinke, to put the current rash of resignations into historical context. The reasons members of Congress give for stepping aside can tell us a lot about the political era in which they occurred, including our own.

The 115th Congress owes its historic turnover to the confluence of two events, one normal and one abnormal. First, there’s the start of a new presidential administration. Five of the first six members to resign this session did so to accept jobs in President Trump’s administration. That’s not unusual. It’s similar to the seven members who resigned in 2009 to join the Obama administration and the five members who left in 1993 to join Bill Clinton’s.

But in addition, three of the four most recent members to resign from the 115th Congress did so because they were accused of unwanted sexual advances: John Conyers, Trent Franks and Al Franken. (Ruben Kihuen, Blake Farenthold and Pat Meehan have announced they will not run for re-election for the same reason. However, a retirement from Congress at the end of one’s regularly scheduled term is not the same as a mid-session resignation, which is what we’re looking at here.)

The extraordinary string of sexual misconduct allegations over the past few months has led many people to conclude we are in the midst of an unprecedented cultural moment. In the political world, at least, the data bears that out. There has never been a concentration of sexual misconduct allegations that has caused as much public fallout before: The number of resignations over non-consensual sexual overtures in the last two months (three) has nearly matched the number in the preceding 116 years (five). And it seems to be a recent phenomenon — the first member to resign for this reason was Bob Packwood in 1995. Admittedly, the data may be skewed; we’re relying partly on news reports for divining members’ reasoning, and sexual misconduct wasn’t exactly a big topic of media coverage for most of the 20th century. Even so, it shows a public reckoning like never before.

In fact, only recently have sex scandals of any nature started to (publicly, at least) cost politicians their jobs. The first member of Congress in the modern era to resign due to an extramarital affair was Wayne Hays in 1976, who paid a former Miss Virginia a congressional salary in exchange for being his mistress. In that case and the next, though, there were extenuating circumstances that made them more than straightforward adultery scandals. Not until Republican Bob Livingston in 1999 did someone resign for a simple affair — and that resignation immediately set off a controversy, as many Democrats protested that it set a precedent for Clinton (who was then in the thick of the Monica Lewinsky scandal) to quit as well. Since then, only one congressman (Mark Souder in 2010) has resigned for the simple act of cheating; four more (including Anthony Weiner’s sexting scandal in 2011 and Tim Murphy pressuring his mistress to have an abortion in 2017) were involved in something more salacious.

But in the big picture, sexual misbehavior, whether consensual or not, has not been a common reason for politicians to resign. Only 3 percent of congressional departures since 1901 have had to do with sex at all, according to media reports.

As shown in the graphic above, other, (mostly) more innocuous reasons have dominated throughout history.

By far the most common reason for members of Congress to resign is that they were voted into other elected offices, such as U.S. senator or governor, or appointed to other government positions, such as a Cabinet or judicial post. Since 1901, this explains 58 percent of departures. The further back you go, the more this reason tends to dominate: From 1901 through 1964, it accounted for three of every four departures. In contrast, since 1965, only 40 percent of departures have been in pursuit of another office.

Changes in how a seat in Congress is valued may explain why this reason has become less dominant as a cause for turnover. Before the days of easy air travel, politicians may have preferred the stability of less-prestigious local offices to the never-ending slog to and from Washington. An even dozen members resigned to become New York Supreme Court justices, all prior to 1969. Five even quit to join their state legislature — four of them before 1946.

Then there are the 15 percent of departing members who were already retiring from office (or had lost re-election) and simply left a little bit early — that is, they resigned at some point between the general election and the end of their term despite not having another gig lined up. In the graphic, you can see huge spikes in this reason in 1966, 1974 and 1978; in each of those years, changes to pension laws made it advantageous for members to resign before Dec. 31 rather than wait until their term expired in early January. (This fact alone explains why the two Congresses with the most resignations, the 93rd and the 95th, are such outliers.) Up until the 1980s, it was also common practice for senators to resign a few days early in order to give their successors a head start on seniority.

An additional 9 percent resigned to take a job in the private sector, such as lobbyist, nonprofit head or media personality. The frequency of this type of resignation has risen noticeably since the 1990s, perhaps because politicians have realized they can cash in on their congressional experience or because an increasingly polarized Congress makes for a less appealing long-term career. Again, though, a bias in the data may be to blame. In categorizing these resignations, we’re at the mercy of media reports and politicians’ public statements, which were less thorough and less critically examined, respectively, the further back they date. We suspect that some older examples of this category may be euphemisms for sins that were never publicly revealed.

Only next do we come to scandals. Six percent of departures were due to non-sex-related scandals such as corruption (the Abscam scandal in 1980–1981, the Jack Abramoff scandal in 2006), illegal-substance possession (alcohol for John Langley in 1926, cocaine for Trey Radel in 2014), or even election fraud (Truman Newberry in 1922, Richard Tonry in 1977).

It seems that another 4 percent of the early exiters left for truly personal reasons: their own failing health (Mo Udall in 1991), the illness of a family member (Geoff Davis in 2012) or to move home to live with their spouse or children (Larry Combest in 2003). We were pretty rigorous about policing all the “to spend more time with family”s out of this category, but it is possible that members who ostensibly resigned for only this reason were hiding something scandalous that was never reported.

Back in the day, it also wasn’t uncommon for Congress to overturn a member’s election after a challenger disputed the result. (As the Constitution says, “Each House shall be the Judge of the Elections, Returns, and Qualifications of its own Members.”) Three percent of our dataset either resigned or were removed from office for this reason — but none since 1938. Nowadays, while ballot-box losers can technically contest an election result before the Senate or House, Congress is much less willing to intercede in the business of counting the votes.

Another three percent of departures stem from unique circumstances that don’t fit in any other category. These range from resigning in protest (the cantankerous Joe Bailey in 1913, Roosevelt-hating James Beck in 1934) to switching parties (Albert Watson in 1965, Phil Gramm in 1983) to major political embarrassment (Newt Gingrich’s spectacular midterm backfire in 1998, Eric Cantor’s out-of-nowhere primary loss in 2014, John Boehner’s exhausting power struggle with the tea party in 2015).

And then there are the 2 percent (13 people) who left Congress to serve their country a different way: in the military. Augustus Gardner resigned to join the Army just a month after the U.S. entered World War I. And during World War II, 12 members left behind their political careers to fight for their country. No one has quit Congress for that reason since.