As Democrats launch their national convention today in Boston, few surprises are likely to surface. Still, if history is any guide, the John Kerry-John Edwards ticket will emerge with a “convention bounce” in the polls. Travis Ridout, an assistant professor in political science at Washington State University who studies the presidential nominating process, said this bounce has averaged about six percentage points since 1964, though its range has been considerable, from nothing for George McGovern in 1972 to 15 percentage points for Bill Clinton in 1992. But Ridout does not expect a large bounce for Kerry this year.  For one, Kerry is already at a better position in the polls than most challengers to an incumbent president at this stage. Second, Kerry has already consolidated the Democratic base. Ridout said that at least 90 percent of Democrats already support the Kerry-Edwards ticket, and thus the campaign has few Democrats to “bring home” through the campaign.  Finally, the TV networks are devoting only three hours of prime-time coverage to the convention, which suggests that direct convention viewership will be low this year. Ridout can be reached at 509.335.2264 or