{"id":295,"date":"2014-10-06T10:11:15","date_gmt":"2014-10-06T08:11:15","guid":{"rendered":"http:\/\/wordpress.callac.online\/index.php\/test-du-chi2-et-test-de-fisher\/"},"modified":"2023-10-14T20:14:39","modified_gmt":"2023-10-14T18:14:39","slug":"test-du-chi2-et-test-de-fisher","status":"publish","type":"page","link":"https:\/\/wordpress.callac.online\/index.php\/logiciels-mathematiques\/le-logiciel-r\/les-tests-avec-r\/test-du-chi2-et-test-de-fisher\/","title":{"rendered":"Test du Chi2 et test de Fisher"},"content":{"rendered":"

Un fichier de donn\u00e9es<\/h2>\n

Travaillons sur une enqu\u00eate de satisfactions dans un h\u00f4pital, r\u00e9cup\u00e9r\u00e9 lors d’un cours de FUN (France Unit\u00e9 Num\u00e9rique). Les fichiers sont disponibles ici<\/a>.<\/p>\n

Par la suite, ces donn\u00e9es seront stock\u00e9es dans la variable satis<\/em> .<\/p>\n

Dans ces donn\u00e9es comme souvent, les observations sont en lignes et les variables en colonnes.<\/p>\n

Pr\u00e9sentation<\/h2>\n\n\n\n\n\n
<\/td>\n$B$<\/td>\n$\\overlineB<\/em>$<\/td>\n<\/tr>\n
$A$<\/td>\n$a$<\/td>\n$b$<\/td>\n<\/tr>\n
$\\overlineA<\/em>$<\/td>\n$c$<\/td>\n$d$<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Dans le tableau pr\u00e9c\u00e9dent, on cherche \u00e0 savoir si le facteur $B$ influe sur le param\u00e8tre $A$.<\/p>\n

Un exemple<\/h2>\n

Cherchons si le sexe des personnes a un r\u00f4le dans le fait de recommander l’\u00e9tablissement.<\/p>\n

Commen\u00e7ons par pr\u00e9parer les variables.<\/p>\n

satis$recommander.b<-ifelse(satis$recommander==2,1,0)<\/pre>\n
On peut alors donner la r\u00e9partition dans un tableau \u00e0 double entr\u00e9e :<\/p>\n
tab<-table(satis$recommander.b,satis$sexe,deparse.level=2) \ntab<\/pre>\n

\nsatis$sexe
\nsatis$recommander.b   0   1
\n0  73  63
\n1 139 130
\n<\/code><\/p>\n
Pour obtenir les pourcentages, utilisons l’instrucion prop.table<\/em>.<\/p>\n
Par d\u00e9faut, elle donne les pourcentages par rapport \u00e1 l’effectif total :<\/p>\n
prop.table(tab)<\/pre>\n

\nsatis$sexe
\nsatis$recommander.b         0         1
\n0 0.1802469 0.1555556
\n1 0.3432099 0.3209877
\n<\/code><\/p>\n
Pour avoir les pourcentages par rapport au total de chaque ligne, on rajoutera margin=1<\/em>, ou margin=2<\/em> pour le total en colonnes.<\/p>\n
prop.table(tab,margin=1)<\/pre>\n

\nsatis$sexe
\nsatis$recommander.b         0         1
\n0 0.5367647 0.4632353
\n1 0.5167286 0.4832714
\n<\/code><\/p>\n
On constate un \u00e9cart entre les deux r\u00e9partitions : l\u00e9g\u00e8rement plus d’hommes (0) recommandent l’\u00e9tablissement. Mais est-ce significatif ?<\/p>\n
Test de Chi2 ou test de fisher ?<\/h2>\n
Par d\u00e9faut, on utilisera le test du Chi2. Mais il faut que les deux conditions suivantes soient respect\u00e9es :<\/p>\n
– des effectifs pas trop petits ;
\n– des pourcentages pas trop extr\u00eames.<\/p>\n
Si ces conditions ne sont pas respect\u00e9es, ce que nous dira le test du Chi2, on utilisera le test de Fisher.<\/p>\n
Les tests avec R<\/h2>\n
Pour le test du Chi2 :<\/p>\n
chisq.test(satis$recommander.b,satis$sexe,correct=FALSE)<\/pre>\n

\nPearson's Chi-squared test<\/code><\/p>\n

\n<\/code><\/p>\n
data:  satis$recommander.b and satis$sexe
\nX-squared = 0.1454, df = 1, p-value = 0.703
\n<\/code><\/p>\n
Pour le test de Fisher :<\/p>\n
fisher.test(satis$recommander.b,satis$sexe)<\/pre>\n

\nFisher's Exact Test for Count Data<\/code><\/p>\n

\n<\/code><\/p>\n
data:  satis$recommander.b and satis$sexe
\np-value = 0.7523
\nalternative hypothesis: true odds ratio is not equal to 1
\n95 percent confidence interval:
\n0.7020996 1.6745388
\nsample estimates:
\nodds ratio
\n1.083487
\n<\/code><\/p>\n
Dans les deux cas, on constate que la p-value<\/em> est trop \u00e9lev\u00e9e (sup\u00e9rieure \u00e0 $5~\\%$.)<\/p>\n","protected":false},"excerpt":{"rendered":"
Un fichier de donn\u00e9es Travaillons sur une enqu\u00eate de satisfactions dans un h\u00f4pital, r\u00e9cup\u00e9r\u00e9 lors d’un cours de FUN (France Unit\u00e9 Num\u00e9rique). Les fichiers sont disponibles ici. Par la suite,…<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":2089,"menu_order":2,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-295","page","type-page","status-publish","hentry"],"yoast_head":"\nTest du Chi2 et test de Fisher - Maths & Num\u00e9rique<\/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:\/\/wordpress.callac.online\/index.php\/logiciels-mathematiques\/le-logiciel-r\/les-tests-avec-r\/test-du-chi2-et-test-de-fisher\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Test du Chi2 et test de Fisher - Maths & Num\u00e9rique\" \/>\n<meta property=\"og:description\" content=\"Un fichier de donn\u00e9es Travaillons sur une enqu\u00eate de satisfactions dans un h\u00f4pital, r\u00e9cup\u00e9r\u00e9 lors d’un cours de FUN (France Unit\u00e9 Num\u00e9rique). 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