Political scientist Alan Abramowitz compares 2010 to 1994 by the number of incumbent vs. open seats and controlling for the partisan tendencies of the districts, and finds that the battle for control of the House could be razor-thin:
While the total number of Democratic House seats is the same today as in 1994, changes in the demographic composition and geographic distribution of the electorate over the past 16 years have resulted in an increase in the number of strongly Democratic House districts. In 1994, Democrats had to defend 87 seats in Republican leaning districts and 55 seats in marginally Democratic districts compared with 114 seats in strongly Democratic districts. This year, in contrast, Democrats must defend only 69 seats in Republican leaning districts and only 42 seats in marginally Democratic districts compared with 145 seats in strongly Democratic districts. Moreover, there are only 15 open seats in Republican leaning or marginally Democratic districts this year compared with 24 in 1994. As a result, even if the Republican tide this year is as strong as it was in 1994, Democrats would lose considerably fewer House seats.
Democrats lost a total of 56 of their previous seats in 1994 while picking up two Republican seats for a net loss of 54 seats. Almost all of the Democratic losses occurred in marginal or Republican leaning districts. Democrats lost 32 percent of their seats with running incumbents in Republican leaning districts and 19 percent of their seats with running incumbents in marginally Democratic districts but only one percent of their seats with running incumbents in strongly Democratic districts. Likewise, they lost 100 percent of their open seats in Republican leaning districts and 75 percent of their open seats in marginally Democratic districts but none of their open seats in strongly Democratic districts.
If we project the 1994 loss probabilities onto the 2010 distribution of Democratic seats in terms of party strength and incumbency status, we would expect Democrats to lose 42 of their current seats in November. Since Democrats are given a good chance of picking up at least three current Republican seats (one each in Hawaii and Louisiana and the at-large seat in Delaware), we would expect a net loss of 39 House seats, leaving Republicans with the narrowest possible majority: 218 seats to 217 for the Democrats.