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1、,第二級,第三級,第四級,第五級,*,第二級,第三級,第四級,第五級,*,四格表的確切概率法,南京醫(yī)科大學(xué)流行病與衛(wèi)生統(tǒng)計(jì)學(xué),柏建嶺,四格表的確切概率法,四格表資料觀察例數(shù)若太小時(shí)，,2,檢驗(yàn)因近似程度較差，易導(dǎo)致分析的偏性,(,尤其是當(dāng)所得概率接近檢驗(yàn)水準(zhǔn)時(shí),),，故宜用四格表的確切概率法,(exact probabilities in 2,2 table),，即四格表概率的直接計(jì)算法。本法不屬,2,檢驗(yàn)范疇，但可作為四格表,2,檢驗(yàn)應(yīng)用上的補(bǔ)充。,基本思想,四格表確切概率的基本思想是：在四格表的周邊合計(jì)不變的條件下，用公式,直接計(jì)算表內(nèi)四個數(shù)據(jù)的各種組合之概率。,單雙側(cè)檢驗(yàn),雙側(cè)檢驗(yàn)時(shí)，需
2、分別計(jì)算兩側(cè)所有,A,-,T,值等于及大于現(xiàn)有樣本,A,-,T,值的四格表的,P,i,值，然后相加，即得雙側(cè)檢驗(yàn)的,P,值。單側(cè)檢驗(yàn)時(shí)，按研究目的只需計(jì)算一側(cè)所有,A,-,T,值等于及大于現(xiàn)有樣本,A,-,T,值的四格表的,P,i,值，然后相加，即為單側(cè)檢驗(yàn)的,P,值。,四格表的確切概率,(Fishers exact probability in 22 table),大腦左半球與右半球的惡性腫瘤作占比例,組別,良性,惡性,合計(jì),惡性腫瘤所占,比例率,(%),左 半 球,13,3,16,18.75,右 半 球,7,6,13,46.15,合計(jì),20,9,29,四格表周邊合計(jì)不變,x,a+b-x,a
3、,+,b,a+c-x,d-a+x,c,+,d,a,+,c,b,+,d,n,x,min,（,a,b,c,d,）,x,=0,1,min,(,a,+,c,a,+,d,),四格表,(,周邊合計(jì)不變時(shí),),所有可能的排列,(1),(2),(3),(4),(5),7,9,8,8,9,7,10,6,11,6,13,0,12,1,11,2,10,3,9,4,|A-T|:,4.0345,3.0345,2.0345,1.0345,0.0345,(6),(7),(8),(9),(10),12,4,13,3,14,2,15,1,16,0,8,5,7,6,6,7,5,8,4,9,|A-T|:,0.9655,1.9655
4、,2.9655,3.9655,4.9655,每一種組合的概率,a,b,a,+,b,c,d,c,+,d,a,+,c,b,+,d,n,超幾何分布,(hypergeometric distribution),超幾何分布,超幾何分布,是統(tǒng)計(jì)學(xué)上一種離散概率分布。它描述了由有限個物件中抽出,n,個物件，成功抽出指定種類的物件的次數(shù),(,不歸還,),。,四格表所有可能排列的概率,(1),(2),(3),(4),(5),7,9,8,8,9,7,10,6,11,6,13,0,12,1,11,2,10,3,9,4,|A-T|:,4.0345,3.0345,2.0345,1.0345,0.0345,P,i,0.0
5、0114,0.01670,0.08909,0.22868,0.31184,(6),(7),(8),(9),(10),12,4,13,3,14,2,15,1,16,0,8,5,7,6,6,7,5,8,4,9,|A-T|:,0.9655,1.9655,2.9655,3.9655,4.9655,P,i,0.23388,0.09595,0.02056,0.00205,0.00007,P,值的計(jì)算,(1),(2),(3),(4),(5),7,9,8,8,9,7,10,6,11,6,13,0,12,1,11,2,10,3,9,4,|A-T|:,4.0345,3.0345,2.0345,1.0345,0.0
6、345,P,i,0.00114,0.01670,0.08909,(6),(7),(8),(9),(10),12,4,13,3,14,2,15,1,16,0,8,5,7,6,6,7,5,8,4,9,|A-T|:,0.9655,1.9655,2.9655,3.9655,4.9655,P,i,0.09595,0.02056,0.00205,0.00007,P=0.225586,超幾何分布的概率分布,Probability,A-T,-4.0345,4.9655,0,.05,.10,.15,.20,.25,.30,.35,結(jié) 論,按,0.05,水準(zhǔn)，不拒絕,H,0,，差異沒有統(tǒng)計(jì)學(xué)意義。故尚不能認(rèn)為大腦兩半球惡性腫瘤所占比例有差別。,
四格表的確切概率法(統(tǒng)計(jì)學(xué))
