2008 First Semester STATS课程官方问答贴

z-score

原帖由 雨轩听风 于 2008-5-3 20:32 发表
阿童木..能不能教我stats125 Assignment 3 Question 5应该怎么做....
题目复制不了...你可以看到我们的ASSIGNMENT..对吧?那就麻烦你了..谢谢......

刚看完题目，你做到哪步骤了？

你integrate那两个function了吗？

c1是从integrate c1(x + 1)^4得到的。

c2是从integrate c2x得到的。

z-score

谢谢，阿我晚了一部。

luvwei

108 assignment 3

q1) we only have one sets of data? and standard error mean wasnt given?
this is a difference between two means right?
why there is only one mean?

and what is Q2 a) asking??

z-score

原帖由 luvwei 于 2008-5-7 14:17 发表
108 assignment 3

q1) we only have one sets of data? and standard error mean wasnt given?
this is a difference between two means right?
why there is only one mean?

and what is Q2 a) asking??

Wow, 这是我在奥大以来第一次问single mean的问题。Question 1不是问difference between two means, 是single mean.

Question 2a是问你哪种situation, situation a, b or c.

luvwei

为什么是今年><
怪不得我看之前的worked example都没有！
照chapter9的第一个example做就可以了吗?
还有，这是不是two tailed test? p value出来的是 只是左边部分的pr 还是左右两边的？

Q2 是situation a没错吧？

谢谢啦~~今天没吃chips??

t-multiplier

原帖由 luvwei 于 2008-5-7 15:18 发表
为什么是今年><
怪不得我看之前的worked example都没有！
照chapter9的第一个example做就可以了吗?
还有，这是不是two tailed test? p value出来的是 只是左边部分的pr 还是左右两边的？

Q2 是situation  ...

Hi luvwei, sorry no English. Yes, it is a two tailed for sure because it said if there is a difference, so it can be both greater or less than. Yep, it is new this year.

Question 2 a should be situation c, because a restaurant could be in both before and after the law change.

No chips for me today.

[ 本帖最后由 t-multiplier 于 2008-5-7 16:41 编辑 ]

z-score

原帖由 雨轩听风 于 2008-5-10 19:19 发表
From his recent experiences of international travel, Tom reckons that the chance of losing luggage on
an international flight is about 1/3 . Assume that this probability remains constant for all ...

a - c绝对都是binomial.

我感觉d是hypergeometric。

mayigo

Suppose that before the minimum wage law change, the underlying mean number of full-time
employees per Burger King restaurant in New Jersey was 11.7. It was thought that the
increase in the New Jersey minimum wage may affect the number of full-time employees in
restaurants. We are interested in investigating if the underlying mean number of full-time
employees per Burger King restaurant in New Jersey is the same after the law change as that
before the law change? To answer this question, the number of full-time employees working
for Burger King after the law change was recorded from the random sample of 129 New
Jersey Burger King restaurants. Summary statistics are displayed below:
                  n           mean                  sd                       
full time       129         10.05                8.129
(a) Carry out a t-test to investigate if the underlying mean number of full-time employees per
Burger King restaurant in New Jersey is the same after the law change as that before the law
change. Interpret your results, including the 95% confidence interval.
Notes:
(i) You must follow the step-by-step guide to performing a t-test by hand given in the
Lecture Workbook, page 9, Chapter 9.
(ii) At step 6 it is necessary to use either a graphics calculator, SPSS, Excel or t-tables to
determine the P-value.
请问lz为什么我题目没有告诉我 the number 和 sd of before the law change just after the law change

z-score

原帖由 mayigo 于 2008-5-12 22:10 发表
Suppose that before the minimum wage law change, the underlying mean number of full-time
employees per Burger King restaurant in New Jersey was 11.7. It was thought that the
increase in the New ...

这道题其实是paired sample t-test, 也就意味着这道题也是one sample t-test.

所以number of restaurants before and after都是一样的。都是129, 这道题你用one sample t-test on a single mean的example作就好了。

mayigo

原帖由 z-score 于 2008-5-12 22:21 发表


这道题其实是paired sample t-test, 也就意味着这道题也是one sample t-test.

所以number of restaurants before and after都是一样的。都是129, 这道题你用one sample t-test on a single mean的examp ...

LZ能告诉我则么写Ho和H1吗？我不是很懂在one sample t-test 应该这么写

z-score

原帖由 mayigo 于 2008-5-12 22:36 发表

LZ能告诉我则么写Ho和H1吗？我不是很懂在one sample t-test 应该这么写

H0: mu = 11.7
H1: mu != 11.7

[ 本帖最后由 z-score 于 2008-5-12 22:58 编辑 ]

mayigo

原帖由 z-score 于 2008-5-12 22:42 发表


H0: mu = 0
H1: mu != 0

请问lz为什么不是H0: mu =50 0
H1: mu != 500 呢？

z-score

原帖由 mayigo 于 2008-5-12 22:48 发表

请问lz为什么不是H0: mu =50 0
H1: mu != 500 呢？

Sorry写错了，应该是11.7.

你在哪里看到的500?

mayigo

原帖由 z-score 于 2008-5-12 22:59 发表

Sorry写错了，应该是11.7.

你在哪里看到的500?

不好意思，我也写错，是11。7

luvwei

108 question one

step four  
is the "estimate" = 10.05? mean number of full time emplyees after law change??

luvwei

原帖由 z-score 于 2008-5-12 22:21 发表


这道题其实是paired sample t-test, 也就意味着这道题也是one sample t-test.

所以number of restaurants before and after都是一样的。都是129, 这道题你用one sample t-test on a single mean的examp ...

isnt it paired sample one sample from chapter 10?
but the question is from chap.9?

is this a single mean question?

z-score

原帖由 luvwei 于 2008-5-13 09:56 发表
108 question one

step four  
is the "estimate" = 10.05? mean number of full time emplyees after law change??

Yes it is.

z-score

原帖由 luvwei 于 2008-5-13 09:58 发表




isnt it paired sample one sample from chapter 10?
but the question is from chap.9?

is this a single mean question?

嗯,这道题是single mean问题.

在stage 1以上的课程里, 老师会教大家怎样用pair t-test算这题, 不过大家不要担心这道题就好了.

z-score

原帖由 yuyu 于 2008-5-13 10:14 发表
question 5
is it X~Poisson(1/4 lamda)?

1/4?

我看题目写的是In a particular 3 month period, 2 fatal snake bites are observed.

lambda应该是2吧.

luvwei

108 question 3
a1 14?
a2?  can u explain it please i dun  really get it???


question three ask us to read section C abt confidence interval and p value. i have read it, but its too complicated...do u have a summarised version that i can understand betterf???


thanksss!!!

z-score

原帖由 luvwei 于 2008-5-13 10:49 发表
108 question 3
a1 14?
a2?  can u explain it please i dun  really get it???


question three ask us to read section C abt confidence interval and p value. i have read it, but its too complic ...

a (i)
Hypothesised value should be 0. The difference between two means should be 0 in the null hypothesis. the 14 is the practical significance part.

(ii) 让你计算standard error (estimate - hypothesised value)/ (sd/sqrt(n))

(c) 完全不用看书，因为看了书也没用。 你看course book Chapter 9还是chapter 10的最后一页. 那个例题就是summary.

luvwei

what happens when p value = 0?

can you please explain statstical significance and practical significance?  im so confused

for ii) i got a negative value. so the direction shoud be to the negative or to the left hhand side right?

luvwei

why cant i see page 20 ??

z-score

原帖由 luvwei 于 2008-5-13 11:16 发表
what happens when p value = 0?

can you please explain statstical significance and practical significance?  im so confused

for ii) i got a negative value. so the direction shoud be to the ne ...

Direction should be either above or below the hypothesised value.

If P-value < 0.05 THEN
statistically significant
ELSE
not statistically significant

If Confidence Interval is within 14, then not practically significant. If CI is outside of 14, then practically significant.If 14 lies within the CI, then we can't tell about its practical significance.

luvwei

so i assume that
b) 1,2,4,5

c i) 1,2,4,5?
  ii)3?

d) 3? how do we knw we have learnd nothing??