I'm confident that this report has crossed Orrin Hatch's desk since this is the group that reports to Congress. I'm sure this applies to the Senate as well. This statistical analysis from March, 1995 shows the historic trend; the incumbent almost always wins. Is this why Hatch has been so cool when faced with solid challenges from the left and right? The only exception to the rule has been that the death of the incumbent, almost always, results in his losing his seat.
Open CRS Network - CRS Reports for the People:Reelection Rates of House Incumbents: 1790 - 1994