Many, but not all, were surprised when Massachusetts Rep. Scott Brown earned the special election victory earlier this year to replace Ted Kennedy. The same group that called that upset also predicted President Obama’s electoral vote total nearly a month before the 2008 election.

That same entity — Dublin, Ireland-based InTrade, an online futures market — now is giving House Republicans a 50-50 chance to reclaim control of their chamber in November.

On Tuesday, April 20 at 4:55 p.m., InTrade’s market for GOP control of the House hit 50.5, meaning traders believed there was a 50.5 percent chance the House would change hands in November. According to CongressDaily:

Analysts at the Wharton School of Business have pegged InTrade’s margin of error at 1 to 1.5 percent, or half that of comparable Gallup polls.

Although one or two major market-makers with deep pockets and an axe to grind can sometimes influence the betting, InTrade has proved to be accurate more often than not. That’s because traders are more likely to do their homework with actual money on the line than with a pollster’s voice on the line, Wharton professors and others argue.

At the close of trading in April 22, Democrats had only a 48.4 percent chance to retain the House. That chance has steadily declined throughout the year but only dropped below 50 percent this week. InTrade’s market for House Republicans picking up at least 35 seats hit 59.5 percent.

The Senate picture is brighter for Democrats, based on InTrade betting. The latest trading puts Senate Democrats’ chances at holding their majority at 77.9 percent. But the market for Republicans picking up at least seven seats stood at 50 percent.