Name the average Lead Margin on  november 13-november 19, 2007?
CREATE TABLE "opinion_polling_for_the_united_states_se" (
  "poll_source" text,
  "dates_administered" text,
  "democrat_larry_la_rocco" text,
  "republican_jim_risch" text,
  "lead_margin" real
);
SELECT AVG("lead_margin") FROM "opinion_polling_for_the_united_states_se" WHERE "dates_administered"='november 13-november 19, 2007';