 He went on to explore other factors that may have explained the effect, such as the use of a likely voter model, and claimed that Rasmussen conducted its polls in a way that excluded the majority of the population from answering.After the 2010 midterm elections, Silver concluded that Rasmussen's polls were the least accurate of the major pollsters in 2010, having an average error of 5.8 points and a pro-Republican bias of 3.9 points according to Silver's model.FiveThirtyEight currently rates Rasmussen Reports with a C+ grade and notes a simple average error of 5.3 percent across 657 polls analyzed.