Is senate polling less reliable than presidential polling?
This is debatable. However, senate races tend to break later than presidential races. Therefore, the degree of uncertainty tends to be higher at a given date before the election; a 10-point lead in the presidential polls in a state tends to be more meaningful than a 10-point lead in the senate polls. The win percentages for senate races are determined based on a historical analysis of senate race data and senate race data only, and apply different parameters than are used in the presidential estimates.
