{"id":265,"date":"2008-11-06T11:55:21","date_gmt":"2008-11-06T19:55:21","guid":{"rendered":"https:\/\/bayesianinvestor.com\/blog\/index.php\/2008\/11\/06\/intrade-versus-fivethirtyeight\/"},"modified":"2010-06-13T18:33:59","modified_gmt":"2010-06-14T02:33:59","slug":"intrade-versus-fivethirtyeight","status":"publish","type":"post","link":"https:\/\/bayesianinvestor.com\/blog\/index.php\/2008\/11\/06\/intrade-versus-fivethirtyeight\/","title":{"rendered":"Intrade versus FiveThirtyEight"},"content":{"rendered":"<p>A number of people have compared the final forecasts for the election (e.g. <a href=\"http:\/\/www.portfolio.com\/views\/blogs\/odd-numbers\/2008\/11\/05\/and-the-winner-isprediction-markets\">this<\/a>), but I&#8217;m more interested in longer term forecasting, so I&#8217;m comparing the state-by-state predictions of <a href=\"http:\/\/www.intrade.com\">Intrade<\/a> and <a href=\"http:\/\/www.FiveThirtyEight.com\">FiveThirtyEight<\/a> on the dates for which I saved FiveThirtyEight data a month or more before the election.<\/p>\n<p>Here is a table of states where Intrade disagreed with FiveThirtyEight on one of the first four dates for which I <a href=\"https:\/\/bayesianinvestor.com\/blog\/index.php\/2008\/09\/07\/intrade-notes\/\">saved<\/a> FiveThirtyEight data or where they were both wrong on July 24. The numbers are probability of a Democrat winning the state&#8217;s electoral votes, with the Intrade forecast first and the FiveThirtyEight forecast second.<\/p>\n<table>\n<tr>\n<td>State<\/td>\n<td>2008-07-24<\/td>\n<td>2008-08-22<\/td>\n<td>2008-09-14<\/td>\n<td>2008-10-01<\/td>\n<\/tr>\n<tr>\n<td>CO<\/td>\n<td>71\/68<\/td>\n<td>60\/53<\/td>\n<td>54.5\/46<\/td>\n<td>67.5\/84<\/td>\n<\/tr>\n<tr>\n<td>FL<\/td>\n<td>42\/29<\/td>\n<td>34.5\/28<\/td>\n<td>30\/14<\/td>\n<td>55.2\/70<\/td>\n<\/tr>\n<tr>\n<td>IN<\/td>\n<td>38\/26<\/td>\n<td>34.1\/15<\/td>\n<td>20\/11<\/td>\n<td>38\/51<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>MO<\/td>\n<td>50\/26<\/td>\n<td>32.9\/13<\/td>\n<td>22.1\/11<\/td>\n<td>42.5\/48<\/td>\n<\/tr>\n<tr>\n<td>NC<\/td>\n<td>30\/22<\/td>\n<td>25\/21<\/td>\n<td>14\/7<\/td>\n<td>51\/50<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>NV<\/td>\n<td>51.2\/49<\/td>\n<td>49\/45<\/td>\n<td>44.9\/32<\/td>\n<td>55\/66<\/td>\n<td><\/td>\n<\/tr>\n<tr>\n<td>OH<\/td>\n<td>65\/53<\/td>\n<td>50\/38<\/td>\n<td>40\/29<\/td>\n<td>53.5\/68<\/td>\n<\/tr>\n<tr>\n<td>VA<\/td>\n<td>60.5\/50<\/td>\n<td>52.3\/36<\/td>\n<td>42\/22<\/td>\n<td>59\/79<\/td>\n<\/tr>\n<\/table>\n<p>On July 24, both sites predicted Florida, Indiana, and North Carolina wrong. FiveThirtyEight got Indiana right on Oct 1 when Intrade was still wrong, but Intrade got North Carolina right on that date (just barely) while FiveThirtyEight rated it a toss-up.<br \/>\nIntrade got Nevada right on July 24 (just barely) while FiveThirtyEight got it wrong (just barely).<br \/>\nFor Virginia, Intrade was right in July and August while FiveThirtyEight was undecided and then wrong.<br \/>\nFiveThirtyEight got Colorado wrong on September 14, but Intrade didn&#8217;t.<br \/>\nFiveThirtyEight got Ohio wrong on August 22, while Intrade got it right.<br \/>\nIntrade rated Missouri a toss-up on July 24, while FiveThirtyEight got it right.<\/p>\n<p>On September 14, FiveThirtyEight was fooled by McCain&#8217;s post convention bounce by a larger margin than Intrade, but by Oct 1 FiveThirtyEight was more confident about correcting those errors.<br \/>\nFor states that were not closely contested, there were numerous examples where Intrade prices where closer to 50 than FiveThirtyEight. It&#8217;s likely that this represents long-shot bias on Intrade.<\/p>\n<p>In sum, Intrade made slightly better forecasts for the closely contested states through at least mid September, but after that FiveThirtyEight was at least as good and more decisive. Except for Intrade&#8217;s Missouri forecast on July 24, the errors seem largely due to underestimating the effects of economic problems &#8211; errors which were also widespread in most forecasts for other things affected by the recession.<\/p>\n<p>In the senate races, I didn&#8217;t save FiveThirtyEight forecasts from before November 1. It looks like both Intrade and FiveThirtyEight made similar errors on the Alaska and Minnesota races.<br \/>\n[Update on 2009-01-13: contrary to initial reports, they apparently got the Alaska and Minnesota races right, although there&#8217;s still some doubt about Minnesota.]<\/p>\n<p>On the other hand, Intrade had been fairly consistently (but not confidently) saying since early July that California&#8217;s Proposition 8 (banning same-sex marriage) would be defeated. Pollsters as a group did a somewhat better job there by issuing conflicting reports.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>A number of people have compared the final forecasts for the election (e.g. this), but I&#8217;m more interested in longer term forecasting, so I&#8217;m comparing the state-by-state predictions of Intrade and FiveThirtyEight on the dates for which I saved FiveThirtyEight data a month or more before the election. Here is a table of states where [&hellip;]<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"jetpack_post_was_ever_published":false,"footnotes":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false,"jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","enabled":false}}},"categories":[17,15],"tags":[36,35],"class_list":["post-265","post","type-post","status-publish","format-standard","hentry","category-if","category-us","tag-2008-election","tag-polls"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p80O1l-4h","_links":{"self":[{"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/265","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/comments?post=265"}],"version-history":[{"count":1,"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/265\/revisions"}],"predecessor-version":[{"id":637,"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/posts\/265\/revisions\/637"}],"wp:attachment":[{"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/media?parent=265"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/categories?post=265"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bayesianinvestor.com\/blog\/index.php\/wp-json\/wp\/v2\/tags?post=265"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}