2008 First Semester STATS课程官方问答贴

z-score

原帖由 阴雨天 于 2008-5-26 19:06 发表
请问ATM 10X的A3 第一题 step 1 parameter是一个single mean 的情况怎么state the parameter??? 谢谢!!

你好，可以这样写, let mu(type the u symbol here) = the underlying..................(basically everything from question)

z-score

原帖由 mumununu 于 2008-5-26 17:43 发表
is 101 assign 3   the last question in 7 f    NO, we can't tell which chain has the highest underlying mean difference ?

你看一下multiple comparisons的output, Wendy's和另外三个(KFC, Burger King and Roy Rogers)比较的P-value都小于0.05, 而且confidence intervals都是正数，所以Wendy's应该是highest mean of them all.

z-score

原帖由 ~kurosaki~ 于 2008-5-26 15:52 发表



thx so much

jst wondering that y there is other ppl says for scenario 4 is Chain as well

is tht right??

I can see why people would say that, because the word Roy Rogers appeared in the question. But in order for a variable to be present, the values of the variable has to change, hence the name of the word variable. We are comparing something from Roy Rogers and something else also from Roy Rogers, so here Roy Rogers doesn't change and hence not variable in nature.

z-score

原帖由 yuyu 于 2008-5-26 20:15 发表
谢谢...

我想问的(b)是:

(b) Let W1,W2, ...,W45 be independent random variables each drawn from the same distribution as W.Let W = (W1+W2+...+W45)/45 . State with parameters the approximate d ...

part b算出来的应该是数字吧？

mumununu

THanks heaps atom, you are the really "Mighty Atom"...

阴雨天

原帖由 z-score 于 2008-5-12 22:42 发表


H0: mu = 11.7
H1: mu != 11.7

null 和 alternative hypothese一样的??? 那P-value interpretation应该怎么写????跟去年相比number of employee变了吗??? 怎么看出来?

z-score

原帖由 阴雨天 于 2008-5-26 21:43 发表

null 和 alternative hypothese一样的??? 那P-value interpretation应该怎么写????跟去年相比number of employee变了吗??? 怎么看出来?

哦，那个!=是not equals to 的意思，=/, 就是这两个符号写在一起。

P-value interpretation可以这样写，we have some evidence that the mean number of employees ......(something something) before the law change is not the same as the mean number of employees ......(something something) after the law change.

Vy2

原帖由 spirithell 于 2008-5-24 18:28 发表
Scenario 1:         Full 2 (qualitative)                State (qualitative)
Scenario 2:         Part 1 (qualitative)                State (qualitative)
Scenario 3: Burger King, StWage1 (quantitative)         Wendy’s, StWage1 (quantitative)
...

S5: shouldn't it be Price 2 and State?? since it's the price of a full meal after the law change and location.

and.. how is Full2 and Part1 quantitative?? they are both numbers of employees..

confuseddddd @.@

z-score

原帖由 Vy2 于 2008-5-26 22:21 发表



S5: shouldn't it be Price 2 and State?? since it's the price of a full meal after the law change and location.

and.. how is Full2 and Part1 quantitative?? they are both numbers of employ ...

Hi, yep, price2 is the price of a full meal after the law change and location (Region) not state tells us the location of the restaurant. Second variable in the variable codebook on page 2 of the assignment. State is either New Jersey or Pennsylvania, not the location that we are interested in.

Yep, both Full2 and Part1 are numerical variables, hence they are quantitative. Right?

Vy2

原帖由 z-score 于 2008-5-26 22:30 发表


Hi, yep, price2 is the price of a full meal after the law change and location (Region) not state tells us the location of the restaurant. Second variable in the variable codebook on page 2 of ...

ok i see now! C= thx so much..
i got confused coz i saw that person's answer..
so just making sure~ ^^

~Kurosagi~

原帖由 z-score 于 2008-5-26 20:15 发表


I can see why people would say that, because the word Roy Rogers appeared in the question. But in order for a variable to be present, the values of the variable has to change, hence the name  ...

i c i c

ldp

108 Question 1

是不是也要求8， Confidence Interval， 那里的那个estimate 也是10.05 还是 10.05 - 11.7 ?

还有第一步我这么说行吗？1， µ = the mean number of full-time employees per Burger King restaurant in New Jersey before the minimum wage law change.

还是只说mean ，不说before & after，我都迷糊了。

还有对下答案， P-value是0.0228 不？

ldp

原帖由 t-multiplier 于 2008-5-23 19:28 发表


We don't know, because the true mean is unknown.

108 Question 1b

这题具体应该怎么说啊？ 就是这么说？能不能给个官方直观说法？实在是不会往题上套了。

z-score

原帖由 ldp 于 2008-5-27 05:34 发表
108 Question 1

是不是也要求8， Confidence Interval， 那里的那个estimate 也是10.05 还是 10.05 - 11.7 ?

还有第一步我这么说行吗？1， µ = the mean number of full-time employees per Burger ...

confidence interval的estimate是sample mean x bar, 10.05. 你写的parameter of interest很好，如果能在mean前面加上一个underlying就够好了。而且要写上before and after.

P-value在印象里差不多0.02.

z-score

原帖由 ldp 于 2008-5-27 05:40 发表





108 Question 1b

这题具体应该怎么说啊？ 就是这么说？能不能给个官方直观说法？实在是不会往题上套了。

The underlying true mean mu (u) is always unknown, because it is a population parameter. The 95% confidence interval is worked out using sample estimates which are known, so we are only 95% sure that over repeated sampling, the underlying mean falls between the 95% confidence interval 95% of the times. So we can't say for sure if the underlying mean is between the interval or not.

ldp

原帖由 z-score 于 2008-5-27 08:33 发表

confidence interval的estimate是sample mean x bar, 10.05. 你写的parameter of interest很好，如果能在mean前面加上一个underlying就够好了。而且要写上before and after.

P-value在印象里差不多0.02.

谢谢阿童木．　要是（a) 1, 写上　before and after, 那不就成要算 the difference了吗？

难道要这样写？　µ = the underlying mean number of full-time employees per Burger King restaurant in New Jersey before and after the minimum wage law change？？？对吗？


还有如果CI　中的　estimate 是１０．０５的话，那
Confidence Interval = 10.05 ± 1.9787 х 0.7157

= (8.63, 11.47)


这样的话。。。
With 95% confidence, we estimate that the underlying mean number of full-time employees per Burger King restaurant in New Jersey before the law change is somewhat between about 8.63 to 11.47 higher than the mean number of full-time employees per Burger King restaurant in New Jersey after the law change.

ldp

还有question 3 (d) 是 case 2 吗？

z-score

原帖由 ldp 于 2008-5-27 08:53 发表




谢谢阿童木．　要是（a) 1, 写上　before and after, 那不就成要算 the difference了吗？

难道要这样写？　µ = the underlying mean number of full-time employees per Burger King restaura ...

哦，对，明白了，不能写before and after, 写after就好了。呵呵。

我开始搞错了，应该是：

With 95% confidence, we estimate that the underlying mean number of full-time employees per Burger King restaurant in New Jersey after the law change is somewhat between  8.63 and 11.47.

[ 本帖最后由 z-score 于 2008-5-27 09:15 编辑 ]

z-score

原帖由 ldp 于 2008-5-27 08:55 发表
还有question 3 (d) 是 case 2 吗？

Nothing useful应该是case 3, 因为它既不是statistically significant而且practical significance is unknown.

ldp

谢谢阿童木了，在确定下，那Ｑ１（a)的第一步是不是就应该写
µ = the underlying mean number of full-time employees per Burger King restaurant in New Jersey after the minimum wage law change．

对不对？

z-score

原帖由 ldp 于 2008-5-27 09:28 发表
谢谢阿童木了，在确定下，那Ｑ１（a)的第一步是不是就应该写
µ = the underlying mean number of full-time employees per Burger King restaurant in New Jersey after the minimum wage law change．
...

是的。 oooOOOO

~Kurosagi~

question 1 a 的step 7 我們要怎么做?

按照course book的jam example來做嗎??

還是??

Vy2

OMG.. what is the validity of the F-test assumptios..???
i found the assumptions for F-test in coursebook..
but validity..??? what am i suppose to do... ><

阴雨天

原帖由 ldp 于 2008-5-27 05:34 发表
108 Question 1

是不是也要求8， Confidence Interval， 那里的那个estimate 也是10.05 还是 10.05 - 11.7 ?

还有第一步我这么说行吗？1， &micro; = the mean number of full-time employees per Burger ...

我的p-value跟你一样！

阴雨天

原帖由 z-score 于 2008-5-26 22:04 发表


哦，那个!=是not equals to 的意思，=/, 就是这两个符号写在一起。

P-value interpretation可以这样写，we have some evidence that the mean number of employees ......(something something) before  ...

原来如此! 谢谢!
还有个问题.step 7 判断observed difference有多statistically的依据是什么??? P-value? 划分的界限分别是什么?

Vy2

原帖由 阴雨天 于 2008-5-27 18:12 发表

原来如此! 谢谢!
还有个问题.step 7 判断observed difference有多statistically的依据是什么??? P-value? 划分的界限分别是什么?

yeah it depends on the p-value.. look at the notes on chapter9 page 11

天外飞猪

atm。。
108第三题为什么只有case3是nothing learned？那case5为什么不是nothing learned?

璐秋孟孟

请问4(a)和5(a)怎么Comment on any features in the plot(s)呢？书里都是dots plot.

阴雨天

求救  101 ASMT Q2(b)我得出的P-value好大啊! 0.756.....
这属于正常情况吗? 还是说我肯定算错了? 我看了一下,得出这么大的P-value 的主要原因是我的T-test的得数是个小于1的数. 是不是说我算错了??  还请做过的朋友告诉我你们的答案是怎样的??