{"id":3726,"date":"2010-03-02T23:32:10","date_gmt":"2010-03-03T04:32:10","guid":{"rendered":"http:\/\/onthe8spot.com\/?p=3726"},"modified":"2010-03-02T23:32:10","modified_gmt":"2010-03-03T04:32:10","slug":"repost-what-is-bayesianism-less-wrong","status":"publish","type":"post","link":"http:\/\/onthe8spot.com\/index.php\/2010\/03\/02\/repost-what-is-bayesianism-less-wrong\/","title":{"rendered":"rePost :: What is Bayesianism? :: Less Wrong"},"content":{"rendered":"<p>I tried explaining this to a friend and ended up in a big argument.\u00a0 It&#8217;s hard to explain things. Communication among human and between animals are awesome when seen in this light.<\/p>\n<blockquote>\n<h1><a href=\"http:\/\/lesswrong.com\/lw\/1to\/what_is_bayesianism\/\">What is Bayesianism?<\/a><\/h1>\n<div class=\"meta clear\"><span class=\"votes\"><span id=\"score_t3_1to\" class=\"votes \">50<\/span><script type=\"text\/javascript\">\/\/ <![CDATA[vl['t3_1to'] = ['49', '50', '51' ];]]><\/script><\/span><span class=\"author\"><a id=\"author_t3_1to\" href=\"http:\/\/lesswrong.com\/user\/Kaj_Sotala\/\">Kaj_Sotala<\/a><\/span><span class=\"date\">26 February 2010 07:43AM<\/span><\/div>\n<p><em>This article is an attempt to <a href=\"http:\/\/lesswrong.com\/lw\/kh\/explainers_shoot_high_aim_low\/\">summarize basic material<\/a>, and thus probably won&#8217;t have anything new for the hard core posting crowd. It&#8217;d be interesting to know whether you think there&#8217;s anything essential I missed, though.<\/em><br \/>\nYou&#8217;ve probably seen the word &#8216;Bayesian&#8217; used a lot on this site, but may be a bit uncertain of what exactly we mean by that. You may have read the <a href=\"http:\/\/yudkowsky.net\/bayes\/bayes.html\">intuitive explanation<\/a>, but that only seems to explain a certain math formula. There&#8217;s a <a href=\"http:\/\/wiki.lesswrong.com\/wiki\/Bayesian\">wiki entry about &#8220;Bayesian&#8221;<\/a>, but that doesn&#8217;t help much. And the LW usage seems different from just the &#8220;Bayesian and frequentist statistics&#8221; thing, too. As far as I can tell, there&#8217;s no article explicitly defining what&#8217;s meant by Bayesianism. The core ideas are sprinkled across a large amount of posts, &#8216;Bayesian&#8217; <a href=\"http:\/\/lesswrong.com\/tag\/bayesian\/\">has its own tag<\/a>, but there&#8217;s not a single post that explicitly comes out to make the connections and say &#8220;<strong>this<\/strong> is Bayesianism&#8221;. So let me try to offer my definition, which boils Bayesianism down to three core tenets.<br \/>\nWe&#8217;ll start with a brief example, illustrating Bayes&#8217; theorem. Suppose you are a doctor, and a patient comes to you, complaining about a headache. Further suppose that there are two reasons for why people get headaches: they might have a brain tumor, or they might have a cold. A brain tumor always causes a headache, but exceedingly few people have a brain tumor. In contrast, a headache is rarely a symptom for cold, but most people manage to catch a cold every single year. Given no other information, do you think it more likely that the headache is caused by a tumor, or by a cold?<br \/>\nIf you thought a cold was more likely, well, that was the answer I was after. Even if a brain tumor caused a headache every time, and a cold caused a headache only one per cent of the time (say), having a cold is so much more common that it&#8217;s going to cause a lot more headaches than brain tumors do. Bayes&#8217; theorem, basically, says that if cause A might be the reason for symptom X, then we have to take into account <em>both<\/em> the probability that A caused X (found, roughly, by multiplying the frequency of A with the chance that A causes X) <em>and<\/em> the probability that <em>anything else<\/em> caused X. (For a thorough mathematical treatment of Bayes&#8217; theorem, see Eliezer&#8217;s <a href=\"http:\/\/yudkowsky.net\/bayes\/bayes.html\">Intuitive Explanation<\/a>.)<br \/>\nThere should be nothing surprising about that, of course. Suppose you&#8217;re outside, and you see a person running. They might be running for the sake of exercise, or they might be running because they&#8217;re in a hurry somewhere, or they might even be running because it&#8217;s cold and they want to stay warm. To figure out which one is the case, you&#8217;ll try to consider which of the explanations is true most often, and fits the circumstances best.<br \/>\nvia <a href=\"http:\/\/lesswrong.com\/lw\/1to\/what_is_bayesianism\/\">Less Wrong: What is Bayesianism?<\/a>.<\/p><\/blockquote>\n<p><!-- .meta --><\/p>\n","protected":false},"excerpt":{"rendered":"<p>I tried explaining this to a friend and ended up in a big argument.\u00a0 It&#8217;s hard to explain things. Communication among human and between animals are awesome when seen in this light. What is Bayesianism? 50Kaj_Sotala26 February 2010 07:43AM This article is an attempt to summarize basic material, and thus probably won&#8217;t have anything new &hellip; <\/p>\n<p class=\"link-more\"><a href=\"http:\/\/onthe8spot.com\/index.php\/2010\/03\/02\/repost-what-is-bayesianism-less-wrong\/\" class=\"more-link\">Continue reading<span class=\"screen-reader-text\"> &#8220;rePost :: What is Bayesianism? :: Less Wrong&#8221;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[79],"tags":[],"class_list":["post-3726","post","type-post","status-publish","format-standard","hentry","category-reposts"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/posts\/3726","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/comments?post=3726"}],"version-history":[{"count":0,"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/posts\/3726\/revisions"}],"wp:attachment":[{"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/media?parent=3726"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/categories?post=3726"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/onthe8spot.com\/index.php\/wp-json\/wp\/v2\/tags?post=3726"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}