It’s getting to be special election season again, with an increasingly competitive House race in upstate New York three weeks away and another high-profile one brewing in Nevada – largely thanks to Sharron Angle’s candidacy.

Special elections are often an interesting pastime during the months between regular elections, and because they have the national stage to themselves, they are often parsed to no end for clues about the national political environment.

And, in large part, it’s an exercise in futility.

Political observers note that Republicans took two seats from Democrats in special elections held in 1994 and Democrats took three seats from Republicans in 2008 – both presaging big gains for their parties in the approaching general election. The 2008 gains, in particular, showed how Democrats could win in the South with conservative Democratic candidates like Mississippi’s Travis Childers and Louisiana’s Don Cazayoux. They later used that strategy to win big in November.

But a look at other recent years doesn’t yield as clear a connection.

Republicans lost two seats in 2004 special elections, for example, but went on to win three in the fall general election. And in 2006, Democrats fell short in a pair of high-profile special elections before winning 31 seats in November.

The best example, though, might be the most recent one: 2010. Yes, you can point to Sen. Scott Brown’s (R) win in the special Senate election in Massachusetts as an example of Republican motivation and momentum. But looking at House special elections yields an altogether different picture.

In 2009 and 2010, Democrats actually held two Republican-leaning House districts in upstate New York and Pennsylvania — won by now-former Rep. Scott Murphy (D-N.Y.) and Rep. Mark Critz (D-Pa.) — while taking another toss-up seat from Republicans in the Empire State, won by Rep. Bill Owens (D-N.Y.). (Republicans did win one Democratic seat in Hawaii, but that was because two Democrats split the vote in a three-candidate field. Democrats won the district back last fall.)

After all of that, Republicans turned in one of the biggest electoral triumphs of all time in the House, winning 63 seats and claiming their biggest majority in 60 years.

At the same time, though, they failed to win anything close to a state like Massachusetts at the Senate level (though they did gain six seats), they lost all 10 House races and every statewide office in Massachusetts itself, and two of the special election winners – one Republican and one Democrat – saw their seats flip right back to the other party. And to cap it off, upstate New York, where Democrats so over-performed in the preceding special elections, was perhaps the one area where Republicans had their most success, winning four seats from Democrats.

In other words: even in the areas where the special elections could have been a signal of some local changes, the results were basically voided just a few months later.

In the end, the special elections of 2010 provide a valuable lesson going forward. And that is that these races can tell us certain things – the strength of a candidate, a committee or an issue – but are generally imperfect gauges — at best — for the national political environment.

“If the House special elections in 2006 and 2010 were supposed to serve as barometers for their respective general elections, then neither Nancy Pelosi nor John Boehner would have ever held the Speaker’s gavel,” said one Republican veteran of recent special elections.

The problem, especially at the House level, is that we want to extrapolate the result in one of 435 House seats into the other 434, when oftentimes the result doesn’t even say much about the district where the special election happened.

That’s because specials are low-turnout affairs in which the slightest detail is magnified to a much greater degree than it would be in a regular election. Because of this, special elections can often yield far different results than regular elections would.

“Mechanics and candidates matter a whole hell of a lot more in a special election than in a regular election,” said one Democratic strategist who is also a veteran of multiple special elections. “You can make the race a lot more about the two or three candidates on the ballot.”

Republicans will acknowledge that much of their trouble in special elections in 2008, 2009 and 2010 had to do with poor candidate recruitment. That factor didn’t matter as much, of course, when turnout was normalized and the national environment effectively took over in November 2010 wave election. At that point, any individual candidate matters far less because the spotlight isn’t trained on them in the lead-up to Election Day.

The same can be said for individual issues. Democrats felt that the stimulus bill worked for them in the special election won by Murphy in March 2009, but that was largely due to how the issue was used in the context of that particular campaign -- and the Republican candidate’s mishandling of it. By the time 2010 rolled around, the stimulus was a liability for Democrats and Murphy lost.

Special elections are mostly a nuisance for the national party committees, who know that the results will get blown out of proportion and, as a result, have to devote valuable resources to a race in a single district (one of 435!) simply because it’s the only game in town.

That said, it won’t stop them from learning their own lessons about the coming election — Democrats have used special elections to try out different field programs, for example — and it won’t stop the winning side from trying to exploit the result as a sign of fortitude and political momentum.

But as we get closer to the races in New York’s 26th district on May 24 and Nevada’s 2nd district on Sept. 13, it’s worth remembering that the lessons of these races often aren’t apparent for quite some time — if at all. And trying to glean anything resembling a national trend is often a fool’s errand.

Nevada, in particular, looks like it will be a free-for-all in which anyone can file for free and get themselves on the ballot — a totally different format than any regular election.

New York, meanwhile, is being billed as a test tube for the Democratic message on the GOP’s Medicare cuts (the Democratic candidate has launched an ad on this topic). But privately, Democrats urge that even a poll showing their candidate within five points shouldn’t raise expectations too much and that the district is tough.

If anything, Democrats will learn a little something about their 2012 messaging, but probably very little about their actual prospects — even if they somehow pull off the upset.

And that’s about par-for-course when it comes to special elections.