Here are the results of the U.S. House midterm elections since 1974:
1974 (Ford) -- Democrats gained 49 seats.
1978 (Carter) -- Republicans gained 15 seats.
1982 (Reagan) -- Democrats gained 26 seats.
1986 (Reagan) -- Democrats gained 5 seats.
1990 (Bush I) -- Democrats gained 7 seats.
1994 (Clinton) -- Republicans gained 54 seats.
1998 (Clinton) -- Democrats gained 5 seats.
2002 (Bush II) -- Republicans gained 8 seats.
2006 (Bush II) -- Democrats gained 31 seats.
2010 (Obama) -- Republicans gained 64 seats.
2014 (Obama) -- Republicans gained 13 seats.
Who's going to be the big winner in 2018? It looks right now that it will be the Democrats going this year. Prognosticator Nate Silver at fivethirtyeight.com says there's a 75.5% chance that Democrats will take control of the House (see chart below). They need about 25 seats to do that, and Silver is currently predicting a gain of 35 seats by Democrats.