Were Tuesday’s election results the “blue wave” Democrats were hoping for? Democrats won control of the House of Representatives and won seven governorships. But even with Senate outcomes still unclear in Arizona and Florida, Democrats lost several seats in the Senate, and their gains in state legislative chambers were below the historical average.

Still, Nate Cohn of the New York Times estimated that the Democrats’ national popular vote was likely to be as high or higher than “wave” elections of 1994, 2006 and 2010. Looking at only House races, Dave Wasserman of the Cook Political Report wrote that it was a “powerful, if uneven wave.” Still others point to Senate Democratic wins in red states such as Montana and West Virginia and Democrats’ success in beating several incumbents in suburban GOP strongholds across the country.

What precisely is a “wave” election? Here are four things to know about evaluating electoral waves.

1. There’s no consensus measure

After the 2014 election, I identified no fewer than nine definitions of a congressional wave election. Some used the net number of seats that switched from one party to another, a measure known as the net partisan seat swing. Others narrowly focused on a party’s performance in either toss-up races or races in which a party’s candidates were not expected to win. Still other approaches judged whether the electoral outcomes reflected a dominant national issue or an opportunity to alter the political status quo.

The least consistent definitions of a wave are based on individual races, surprise outcomes or switches in partisan control of legislative chambers. While popular, they should be avoided, since they seldom consider whether those outcomes are historically unusual.

Washington Post reporter Colby Itkowitz examines how these competing definitions of a wave election lead to contradictory conclusions about the 2018 elections. On one hand, she notes, some have insisted it was a wave because of several upsets; the defeats of high-profile Republicans such as Kris Kobach and Scott Walker; and the near-loss of Republican Ted Cruz in Texas. But others insist the opposite, pointing to Democratic losses in the Senate and the failure of high-profile candidates such as Beto O’Rourke to win election.

2. Benchmarking against history is important

If we want a more rigorous definition of a wave, it should account both for actual election outcomes and for the size of a party’s success compared to some historical benchmark. For legislative elections, a good option is to compare net partisan seat swings to past elections. That measure captures an election’s relative impact on legislative politics, since the number of seats a party holds — not the number of votes it received — shapes a party’s agenda and influence.

By this measure, 2018 offers a mixed picture. Since 1902, the historical midterm average House seat gain for the party that does not occupy the White House is 31. House Democrats in 2018 will probably gain 35 to 38 seats when all the counting is done. That suggests a House wave for the Democrats.

But in their analysis of elections dating to 1918, Rob Oldham and Jacob Smith argue that a wave election is one in which the out-party’s seat gain ranks among the top 20 percent of all seat swings over the past century. Oldham and Smith calculate that it would take a much larger swing in the House — 48 seats — to reach that threshold. There aren’t enough undecided House races left that lean Democratic, even slightly, for that to happen this year.

3. Politicians claim they know a wave when they see one

Defining a wave election is not merely academic. As RealClearPolitics staffer Sean Trende has noted, politicians frequently cite electoral waves to claim a voter mandate for bold policy action or to rebuke an opposite-party president. Would Republicans have so zealously tried to enact the Contract With America in 1995, or repeal Obamacare in 2011, had they not interpreted the previous election as a GOP wave?

The lack of consensus about how to define a wave election may encourage politicians to define it as it suits them. In the wake of this week’s election, House Minority Leader Nancy Pelosi (D-Calif.) claimed victory, while President Trump insisted he had “stopped the blue wave.”

4. Elections matter, wave or not

Of course, the debate over what counts as a wave misses the point: Elections may shape national and state policymaking, no matter how big or small a particular party’s win or loss.

For instance, because of last week’s elections, congressional Democrats will be able to hold hearings and conduct investigations into the Trump White House. The elections weakened the GOP’s influence in state-level governance, which will make it harder for Republicans to control redistricting after the 2020 census. Meanwhile, the Senate GOP maintained its ability to confirm the president’s nominations of federal judges and high-level bureaucrats. And the elections increased the diversity of the country’s elected leadership.

These are significant consequences of the 2018 election, whether it was a wave or a ripple.

Matthew Green (@mattngreen) is a professor of politics at Catholic University and the author of “Underdog Politics: The Minority Party in the U.S. House of Representatives” (Yale University Press, 2015).