UK A Level Stats. 求救

我想問下Student's t-distribution同
normal distribution、點樣可以係題目中分辨出黎?

圖上1A、因為係Normally distributed、加上係計Confidence interval (CI)、
所以我知道係用Percentage points of the normal distribution既0.975=1.96做p、
但係bi 同樣地都係計CI、但係睇返MS點解係用Student's t??

同樣地、今次係做Hypothesis test、正常?應該係用Student's t、
點解今次david同james係用normal distribution??

各位數學神手、幫幫手解答呢個問題、
究竟題目中有咩hints可以令你一睇就知條formula係用student's t定normal distribution?

為左方便大家解答、
此link為normal distribution既table:
http://www.cardiff.ac.uk/maths/teaching/probability/Tables/Normal%20Percentage%20Points.html

Student's t-distribution:
http://en.wikipedia.org/wiki/Student's_t-distribution

THANKS A LOT

PS>
以上既題目係由AQA A Level Mathematics Jan 2011 Statistics 2b Question Paper抽出

eric_ah4	2011-12-10 07:19
如果知道真正的variance就應該用normal distribution 如果只係知道sample variance就應該用student t 但下面個題因為sample size比較大,所以都可以用normal distribution When n increases, critical value of student t is near to normal

托利斯

2011-12-10 07:44

引用第1樓eric_ah4於2011-12-10 07:19發表的“”:
如果知道真正的variance就應該用normal distribution
如果只係知道sample variance就應該用student t
但下面個題因為sample size比較大,所以都可以用normal distribution
When n increases, critical value of student t is near to normal

即係好似第1a同5aii咁比左個(s^2)=variance、就用normal distribution?
要自己計就students t?
老師教過n>30就 = central limit theorem

搞左成年、都唔係好識分咩叫population同sample size

kamch116	2011-12-10 07:46
S2黎?? 我都唔識

托利斯	2011-12-10 07:48
*引用第3樓kamch116於2011-12-10 07:46發表的“”*: S2黎?? 我都唔識 [表情] 對

托利斯

2011-12-10 08:01

Jan呢個stat食蕉都似

今日做條pp關於contingency table個陣、
見到有條咁樣

心諗easy job、degrees of freedom (v)=4，點知一睇ms o哂咀，
原來計哂每項既Ei之後、如果Ei<5 要combine 2個categories

16-17同18-21要結合做16-21、跟住50-65同Over 65就結合做Over 50、最後變左v=2
又唔知老師係唔講定唔記得講、冇個神人提一提、
呢條就捧蛋、連跌2/3個grade都似

fatman	2011-12-10 10:19
*引用第5樓托利斯於2011-12-10 08:01發表的“”*: Jan呢個stat食蕉都似 [表情] [表情] 今日做條pp關於contingency table個陣、見到有條咁樣 ....... 我就咁睇都以為12分咁簡單

eric_ah4	2011-12-10 15:05
*引用第2樓托利斯於2011-12-10 07:44發表的“”*: 即係好似第1a同5aii咁比左個(s^2)=variance、就用normal distribution? 要自己計就students t? 老師教過n>30就 = central limit theorem ....... 唔關係唔係自己計出黎事總之只知道sample var就用student t

kamch116	2011-12-11 07:13
你搞到我都好驚S2喎真係要係XMAS操下先

托利斯	2011-12-11 08:50
*引用第8樓kamch116於2011-12-11 07:13發表的“”*: 你搞到我都好驚S2喎 [表情] 真係要係XMAS操下先其實唔係難、不過要好搞清d concept(use of formula), same as econ

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