{"id":7381,"date":"2012-05-11T08:44:40","date_gmt":"2012-05-11T06:44:40","guid":{"rendered":"http:\/\/www.ziserman.com\/blog\/?p=7381"},"modified":"2012-05-11T08:44:40","modified_gmt":"2012-05-11T06:44:40","slug":"tests-ab","status":"publish","type":"post","link":"https:\/\/www.ziserman.com\/blog\/2012\/05\/11\/tests-ab\/","title":{"rendered":"Tests AB"},"content":{"rendered":"<blockquote><p><em>Cet article a \u00e9t\u00e9 r\u00e9dig\u00e9 par <a href=\"http:\/\/fr.linkedin.com\/in\/florentempis\" target=\"_blank\">Florent<\/a><\/em><\/p><\/blockquote>\n<p>Aujourd&rsquo;hui, on ressort les calculettes et nos formulaires de statistiques!<\/p>\n<div>Beaucoup d&rsquo;entre vous ont entendu parler de tests A\/B, voire les pratiquent d\u00e9j\u00e0. Mais \u00eates-vous s\u00fbr de bien interpr\u00e9ter les r\u00e9sultats?<\/div>\n<div><\/div>\n<div>Les tests A\/B sont une technique statistique o\u00f9 on pr\u00e9sente al\u00e9atoirement deux versions d&rsquo;un m\u00eame \u00e9l\u00e9ment: par exemple, une page d&rsquo;accueil avec une photo ou une page d&rsquo;accueil avec des vid\u00e9os.<\/div>\n<div>Ces tests sont pratiqu\u00e9s depuis le d\u00e9but des ann\u00e9es 2000, le premier test de grand ampleur connu a \u00e9t\u00e9 r\u00e9alis\u00e9 par Google pour d\u00e9terminer le nombre optimal de r\u00e9sultats par page (la r\u00e9ponse fut 10!).<\/div>\n<div><\/div>\n<div>Le plus souvent, on pr\u00e9sent ces tests avec ce que l&rsquo;on appelle un intervalle de confiance, sous cette forme: \u00ab\u00a0Nous sommes \u00e0 95% certains que A est plus performant que B\u00a0\u00bb<\/div>\n<div>Pour arriver \u00e0 cette conclusion, il faut valider un certain nombre de choses auxquelles nous ne pensons pas toujours:<\/div>\n<div>\n<ul>\n<li>Sommes-nous certains que A et B sont strictement ind\u00e9pendants?<\/li>\n<li>Sommes-nous certains que les populations expos\u00e9es \u00e0 A et B sont r\u00e9ellement semblables (par exemple, envoyer tous les clients espagnols vers la version A et tous les clients belges vers la version B: qui dit que les espagnols r\u00e9gissent de la m\u00eame fa\u00e7on \u00e0 une video que les belges?)<\/li>\n<li>Quand faut-il arr\u00eater le test?<\/li>\n<\/ul>\n<div>C&rsquo;est bien souvent sur cette derni\u00e8re question que les tests AB p\u00eachent. En effet, pour assurer la validit\u00e9 statistique, il faut en th\u00e9orie au pr\u00e9alable d\u00e9finir le nombre de tests. Deux probl\u00e8mes \u00e0 cela: sur des \u00e9l\u00e9ments \u00e0 faible trafic, il est parfois long d&rsquo;atteindre le nombre correspondant au seuil de confiance fix\u00e9 (95 ou 99% g\u00e9n\u00e9ralement). L&rsquo;autre probl\u00e8me est qu&rsquo;on expose parfois 50% de ses visiteurs \u00e0 un \u00e9l\u00e9ment qui convertit extr\u00eamement mal! Perdre deux points de taux d&rsquo;engagement sur 50% de son trafic pendant 1 jour, 1 semaine ou 1 mois, cela peut donner lieu \u00e0 des pertes financi\u00e8res tr\u00e8s importantes!<\/div>\n<\/div>\n<div><\/div>\n<div>Plusieurs solutions sont possibles mais leur d\u00e9monstration sort du cadre de cet article.<\/div>\n<div>L&rsquo;une est d&rsquo;utiliser un d\u00e9riv\u00e9 du test du khi-2 (le G-Test) sur les variables (qui permettra de v\u00e9rifier que l&rsquo;on n&rsquo;est pas dans un cas ind\u00e9cidable), l&rsquo;autre est de prendre une approche dite bay\u00e9sienne (qui permettra de stopper l&rsquo;exp\u00e9rience d\u00e8s que la r\u00e9ussite de A est sup\u00e9rieure \u00e0 celle de B d&rsquo;un certain seuil)<\/div>\n<div><\/div>\n<div>Enfin, et c&rsquo;est l\u00e0 le plus important, vos tests doivent \u00eatre solides, de mani\u00e8re \u00e0 se d\u00e9faire d&rsquo;un d\u00e9faut malheureusement tr\u00e8s courant dans les processus de d\u00e9cision: l&rsquo;avis du plus haut salaire est consid\u00e9r\u00e9 comme le meilleur: \u00ab\u00a0Highest-Paid Person Opinion\u00a0\u00bb, ou HiPPO.<\/div>\n<div>Cet article r\u00e9cent de Wired en est la parfaite illustration: les dirigeants d&rsquo;Amazon ne croyaient pas aux recommendations pour l&rsquo;achat d&rsquo;impulsion, les donn\u00e9es leur ont montr\u00e9 qu&rsquo;ils avaient tort!<\/div>\n<div><a href=\"http:\/\/www.wired.com\/epicenter\/2012\/04\/ff_abtesting\/all\/1\" target=\"_blank\">http:\/\/www.wired.com\/<wbr>epicenter\/2012\/04\/ff_<wbr>abtesting\/all\/1<\/wbr><\/wbr><\/a><\/div>\n<div><\/div>\n<div>Si le sujet des statistiques appliqu\u00e9es au marketing vous int\u00e9resse, un prochain article suivra sur le Multi Variable Testing, ses contraintes et ses applications.<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Cet article a \u00e9t\u00e9 r\u00e9dig\u00e9 par Florent Aujourd&rsquo;hui, on ressort les calculettes et nos formulaires de statistiques! Beaucoup d&rsquo;entre vous ont entendu parler de tests A\/B, voire les pratiquent d\u00e9j\u00e0. Mais \u00eates-vous s\u00fbr de bien interpr\u00e9ter les r\u00e9sultats? Les tests A\/B sont une technique statistique o\u00f9 on pr\u00e9sente al\u00e9atoirement deux versions d&rsquo;un m\u00eame \u00e9l\u00e9ment: par [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"footnotes":""},"categories":[2],"tags":[373,180],"class_list":["post-7381","post","type-post","status-publish","format-standard","hentry","category-e-commerce","tag-e-marketing","tag-taux-de-transformation"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.2 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Tests AB - Ziserman.com<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.ziserman.com\/blog\/2012\/05\/11\/tests-ab\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Tests AB - Ziserman.com\" \/>\n<meta property=\"og:description\" content=\"Cet article a \u00e9t\u00e9 r\u00e9dig\u00e9 par Florent Aujourd&rsquo;hui, on ressort les calculettes et nos formulaires de statistiques! Beaucoup d&rsquo;entre vous ont entendu parler de tests A\/B, voire les pratiquent d\u00e9j\u00e0. Mais \u00eates-vous s\u00fbr de bien interpr\u00e9ter les r\u00e9sultats? 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