Complex sentence: Various estimates have been made to sift through the data and discern how many votes incumbency itself is worth, and although various methodologies have yielded varied results it has been estimated that prior to the mid- 1960s incumbency added only a few percentage points to the incumbents column.
Split into simpler sentences: Various estimates have been made to sift through the data and dicern how many votes incumbency itself is worth. Although various methodologies hae yielded varied results it has been estimated that prior to the mid- 1960s incumbency added only a few percentage points to the incumbents column.