The C-SPAN networks are available in more than 100 million households as of 2010[update], not including access to the C-SPAN websites.[50][130] More than 7,000 telephone callers have participated with discussion on Washington Journal as of March 18, 2009[update].[131] There are no official viewing statistics for C-SPAN because the network, which has no commercials or underwriting advertisements, does not use the Nielsen ratings.[4] However, there have been a number of surveys providing estimates: