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标题: 2008 First Semester STATS课程官方问答贴 [打印本页]
作者: z-score    时间: 2008-2-28 19:42:54     标题: 2008 First Semester STATS课程官方问答贴

阿童木会在奥大板块长期提供STATS课程的免费问答。本贴为大家提供assignment, course book, test & exam questions的帮助。

阿童木可以帮助的统计课程:

10x (4楼)
125 (5楼)
20x (6楼)
210 (7楼)
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326 (10楼)
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为了方便大家，阿童木把不同课程的宝贵学习资料放到它们对应的帖子里。

本贴宗旨:

为人民服务，推广全民统计普及。

注意:

请大家在问问题前看一下2楼的贴规。

后缀:

想直接得到assignment答案的人们可以去assistance room或lab找为了省事直接给学生答案的tutor们，阿童木在这里会帮助想真正理解统计的朋友们去思考，得到最后的答案。

[ 本帖最后由 z-score 于 2008-3-28 12:15 编辑 ]
作者: z-score    时间: 2008-2-28 19:47:04     标题: 本贴的贴规


谢谢大家的合作

阿童木祝各位朋友在本学期的统计课程中得到满意的成绩。


[ 本帖最后由 z-score 于 2008-3-14 14:35 编辑 ]
作者: z-score    时间: 2008-2-28 19:47:34     标题: 2008 Summer School问答贴中的宝贵信息

这里的问题都是我在Summer School问答贴回答过的

为了阅读的方便，问题标为蓝色，回答标为红色。

20x General Questions

odds ratio是不是只需要知道怎麽寫executive summary?

是的，因为odds ratio的technical notes就是R code.

1e-3=0.001?

是的。

20x Tutorial Questions

Tutorial 10 ADD data:

"The plot of Cook’s distance shows none of the observations have an undue influence
on the final model. Observation 78 has a large value of Cook’s distance, relative to the
other observations, but removing it did not change any of the coefficients by more
than a standard error, so it was retained."

是怎么看删去unusual observations后，有没有SIGNIFICANT CHANGE呀？
还有。所说的“did not change any of the coefficients by more than a standard error”是怎么看出来的？

new coefficient - old coefficient
- -！是全部的VARIABLE都要试过去吗？
你能拿这个例子示范一下怎么算给我看吗？谢谢。

> exam.fit3<-lm(Exam~Assign+Test+I(Test^2)+Stage1,
data=course.df[-106,])
> summary(exam.fit3)
Coefficients:
                    Estimate   Std. Error t value Pr(>|t|)
(Intercept)     31.42284 6.37936    4.926  2.35e-06 ***
Assign          1.35513 0.24074 5.629 9.65e-08 ***
Test             -0.83163 1.11701 -0.745 0.45782
I(Test^2)      0.12584 0.04633 2.716 0.00745 **
Stage1B       -5.22603 2.19378 -2.382 0.01856 *
Stage1C       -12.78126 2.34233 -5.457 2.16e-07 ***

> summary(exam.fit2)
                 Estimate   Std. Error t value Pr(>|t|)
(Intercept)  30.69567 6.49900    4.723 5.58e-06 ***
Assign        1.56651   0.23068    6.791 2.93e-10 ***
Test           -1.24720 1.12706     -1.107 0.27036
I(Test^2)    0.13846   0.04698    2.947 0.00376 **
Stage1B     -4.45745  2.21620    -2.011 0.04621 *
Stage1C     -11.84911 2.35973   -5.021 1.54e-06 ***

IF((new coefficient - old coefficient)/old standard error)>1
THEN influential

除了intercept

Assign (1.56651-1.35513)/0.24074=?

下面的test, test2, stage1B和stage1C都要试，如果很多都是>1, 106就是influential.

还有。。。我刚才看CASE STUDY ：PERUVIAN INDIANS。。
((new coefficient - old coefficient)/old standard error) 如果是-1 -2什么的是不是也算？
因为我算了下 weight是(0.82103-1.263)/0.31261=-1.4139

嗯，是的，是绝对值。

Tutorial 11: Logistic Regression & Time Series
Meningitis Data那道题。。。

Using the output from the seasonal factor model (page 506), calculate the forecast of
the log of the number of notified cases of meningitis for January 1998.

The seasonal factor log model is:
log.meningitist = 0.628026 + 0.019481 × time – 0.252158 × month2 + … +
0.064355 × month12 + 0.321058 × log.meningitist-1

We are forecasting for January 1998 i.e. time period 97
log.meningitis97 = 0.628026 + 0.019481 × 97 – 0.252158 × 0 + … +
0.064355 × 0 + 0.321058 × log.meningitis96

= 0.628026 + 0.019481 × 97 – 0.252158 × 0 + … +
0.064355 × 0 + 0.321058 × 3.988984
= 3.798378225

我想知道。。。log.meningitis96也就是 3.988984是怎么得出来的？

不是题目里面的54吗？你log(64)=3.988984

20x Past Exam Questions

PAST EXAM PAPER....2007 S2....SECTION A.......
QUESTION 7&10...怎麽算答案都不對....阿童木能演算一下嗎?謝謝...

Question 10

> exp(log((35*155)/(129*11))-1.96*sqrt(1/35+1/11+1/129+1/155))
[1] 1.867189

Answer is the first 1.

Question 7

> exp(2.797203+0.010852*85+0.509277*log(104660))
[1] 14854.93

Answer is the fourth 1.

我想問一下....2007 S1
question 3 為什麽選項3是錯的?
question 7 為什麽選項2是錯的?還有第3個和第5個選項是怎麽算出來的...
question 14 爲什麽選項1是錯的?

謝謝

2007S1
Question 3

(3)We estimate that the odds of dying for a patient admitted to ICU withan infection are about 0.77 times the odds for a patient admittedwithout an infection.

Coefficients:
        Estimate Std. Error z value Pr(>|z|)
INF  0.76525  0.41681   1.836   0.066360 .

> exp(0.76525)
[1] 2.149532

得到odds需要back-transform. 0.77没有transform.

Question 7

Coefficients:
             Estimate     Std. Error  t value    Pr(>|t|)
time[-1] 1.194e-02   1.792e-03  6.664      9.77e-11 ***

2) For each additional unit of time, the CO2 concentration increases by about 0.012 ppm, on average.

这句是错的因为不是the CO2 concentration increases by about 0.012, 是the mean CO2 concentration increases by about 0.012.

(3) We estimate that the autocorrelation coefficent (rho) is about 0.78

Coefficients:
                         Estimate     Std. Error  t value    Pr(>|t|)
dioxide.ts[-384]   7.777e-01  3.289e-02  23.648    < 2e-16 ***

7.777e-01, 这个是estimated rho.

(5) A point estimate for the difference in average CO2 concentrationbetween July and August of each year is about 0.887 ppm, having allowedfor the trend and for autocorrelation.

Coefficients:
                         Estimate     Std. Error  t value    Pr(>|t|)
month[-1]7        -1.636e+00 1.273e-01  -12.846 < 2e-16 ***
month[-1]8        -2.523e+00 9.083e-02  -27.782 < 2e-16 ***

> -2.523--1.636
[1] -0.887

Question 14

(1) A high value for R2 indicates that our model will be useful for prediction.

A regression model will only be useful for prediction if and only ifthe R2 is high and having satisfied the normality assumption.

2007 SS
question 9
option 1是怎麽算出來的?
option 5為什麽是錯的?

2007SS Question 9

(1) Using the regression model, our point prediction for the 1st quarter 2003 is about 15.4 million litres.
> beer.pred
                fit             upr           lwr
2003 Q1 15224.24 19383.60 11064.886

15224大约等于15.4million.

(5) The point prediction for the 4th quarter of 2004, using theregression model does not lie within the prediction interval weobtained using the Holt-Winters technique.

在Holt-winters, point estimate是C.I.的中间值。所以does not lie within是错的。

thanks...

For 2006 Second semester ...
question 10. how to get the answers for option 4 and 5?

2006SC Question 10

> predictions
                fit               upr             lwr
Jan 1973 0.3860656 0.7937101 -0.021578940

(4) Our point prediction for ozone concentration for January 1973 is about 1.47 ppm.

(5) We estimate ozone concentration for January 1973 will be between 0.98 ppm and
2.21 ppm.

> exp(c(0.3860656,0.7937101,-0.021578940))
[1] 1.4711812 2.2115864 0.9786522

For first semester 2006
question 5
the option 2
why we cannot qualify the difference in average ages using this analysis?

That's because the analysis was done on the transformed data.

summer school 2006
question 18 b) 爲什麽是用chi-square test...hourly attendance不是quantitative variable嗎?

因为这是一个trick, hourly attendance你就record(count)一次，所以你没有quantiative variable, it's not a variable, it's only a count.

2007 S2
Q9 option 4 是怎么算的？谢谢

2007SC Question 9

(4) We estimate that if a patient required resuscitation, the odds of survival are
multiplied by about 0.2

Coefficients:
              Estimate Std. Error z value Pr(>|z|)
CPR     -1.63066 0.61553   -2.649  0.00807 **

> exp(-1.63066)
[1] 0.1958003

我又来了~

想问一下..2006 SUMMER SCHOOL的QUESTION 8
为什么第一个选项是对的...第二个是错的?

2006 SS
Question 8

(1) The residuals appear to be reasonably symmetric.

Residuals:
Min           1Q             Median     3Q           Max
-0.060829 -0.013325 0.002093 0.012705 0.047020

5 number summary shows the residuals appear to be symmetric.

(2) The t-statistic for testing the hypothesis that there is no trend is about 6 million litres.

Coefficients:
                 Estimate     Std. Error   t value Pr(>|t|)
time[-1]    0.0016375 0.0002039 ***** 2.43e-13 ***

t = > 0.0016375/ 0.0002039
[1] 8.030897

2007 SS
question 10:
爲什麽第一個選項是對的,第二個選項是錯的?

還有就是question 18不是會讓我們選擇which form of analysis should be used to investigate嗎?
在什麽情況下  我們會用到logistic regression?

2007SS

(1)The confidence interval for the odds of dying for patients admitted ina semiconscious state compared to the odds of dying for patientsadmitted in a conscious state will contain 1
Coefficients:
            Estimate   Std. Error    z value Pr(>|z|)
LOC1   18.60221 1039.99658 0.018  0.985729

The P-value 0.985729 refers to the hypothesis that the log oddsassociated with LOC1 is zero. After backtransforming, exp(0) = 1, sothe confidence interval should contain 1 as an insiginificant P-valuecontains the hypothesised value.

(2) For each additional year of age of patients admitted to ICU, the odds of dying increase by about 0.03

Coefficients:
         Estimate Std. Error z value Pr(>|z|)
AGE  0.03072 0.01268   2.423  0.015377 *

The log odds increases by about 0.03, not the odds.

For question 18, you use logistic regression when your response variable is qualitative binary variable.

[ 本帖最后由 z-score 于 2008-2-28 21:11 编辑 ]
作者: z-score    时间: 2008-2-28 19:47:41     标题: 10x的学习资料与问题回复

学习资料附件的解释:

STATS10x Worked Examples - 阿童木的例题工作过程

[ 本帖最后由 z-score 于 2008-9-11 21:32 编辑 ]
作者: z-score    时间: 2008-2-28 19:47:59     标题: 125问题的回复

学习资料附件的解释:

[ 本帖最后由 z-score 于 2008-9-11 21:32 编辑 ]
作者: z-score    时间: 2008-2-28 19:48:05     标题: 20x的学习资料与问题回复

学习资料附件的解释:

STATS20x.zip - 本学期所有的assignment数据

STATS20x Worked Examples - 阿童木的例题工作过程

[ 本帖最后由 z-score 于 2008-9-11 21:34 编辑 ]
作者: z-score    时间: 2008-2-28 19:48:31     标题: 326问题的回复

更新中

[ 本帖最后由 z-score 于 2008-3-14 11:31 编辑 ]
作者: z-score    时间: 2008-2-28 19:48:41     标题: STATS课程辅助资料

更新中

[ 本帖最后由 z-score 于 2008-2-28 20:12 编辑 ]
作者: z-score    时间: 2008-2-28 19:56:54     标题: Second semester copy & paste

更新中

Study 3: A road safety researcher was interested in the effects ofalcohol on the driving ability of young adults. A sample of 50 youngadults was obtained and each was randomly allocated to either analcohol group or a no alcohol group. The members of the alcohol groupeach drank 700ml of beer then did a 10 minute session on a drivingsimulator. The members of the no alcohol group just did a 10 minutesession on a driving simulator. For each member, the driving simulatorreported the number of errors made during their 10 minute session.

(d) For study 3, students had differing drinking histories, with somebeing heavy drinkers, some being moderate drinkers and some being milddrinkers.
Consider the statement: “The two groups of students in study 3__________ roughly balanced with respect to previous drinking history.”
Which one of the following phrases would best fill in the missing gap in the statement?
“will be” “are likely to be” “are not likely to be” “wont be”
Briefly justify your choice.

他都没有说作出来结果是怎样，要怎么决定？他是不是
ballance

帮帮我吧

嗯，这个问题问得很好。你考虑问题里的这点:

Study 3: A road safety researcher was interested in the effects ofalcohol on the driving ability of young adults. A sample of 50 youngadults was obtained and each was randomly allocatedto either an alcohol group or a no alcohol group. The members of thealcohol group each drank 700ml of beer then did a 10 minute session ona driving simulator. The members of the no alcohol group just did a 10minute session on a driving simulator. For each member, the drivingsimulator reported the number of errors made during their 10 minutesession.

为什么我们要randomly allocate？

因为我们知道所有的驾驶者能分为三种，他们承受酒精的能力不同，这会影响最重的结果。randomallocation方法 wishes to achieve a fair and balanced comparison betweendifferent groups. 意思是说，随即的取样可以试图得到balanced samples。

如果我们再考虑一下，在统计里，我们能有will be吗？（能有绝对性吗？) 同样，我们能有won't be吗？（绝对不可能）

所以答案应该是？


SELF-SELECTION BIAS。AND THE SELECTION BIAS。。好像大同小异。。我看概念了。。。 可真正区分要犹豫好久。。才能判断出。。  请你讲解下哦 。。 谢谢。。。

Selection bias和self selection bias的最大区别是selection bias是在一个sample里出现，self selection没有一个固定的sample。

Selection bias指的是你的sample与population of interest不一样。

Self selection bias指的是当你没有一个固定的sample下，那些自愿参加调查人所带来的偏差。


我有一个问题啊:
1.observation studies 和 experiments有什么不同? 请分别给解释一下 谢谢



Experiments可以randomly allocate subjects, 意思是说如果你从新再搞一次试验，在A组的人或东西可以变为B组的人或东西。每次试验，不同组的组合纯属依靠几率。

Observational study的不同组不能改变，举例子: 比较男女或老少。男就是男，不是我们randomly allocate给他的。如果老就是老，不是我们给他的年龄。

sampling error 和 non-sampling error的解释好象Course book上并没有明确指出 就麻烦LZ了! 谢谢

这是一个很好的问题。

你来想象一个飞镖与飞镖盘。

假设你扔了4个飞镖，你这4个飞镖的中心与飞镖盘的圆心的距离就是non-sampling error。

你这4个飞镖与这4个飞镖中心的距离就是sampling error。

[ 本帖最后由 z-score 于 2008-4-1 11:13 编辑 ]
作者: 萨米    时间: 2008-2-28 20:11:49

我也留一个
作者: 萨米    时间: 2008-2-28 20:11:58

我再留一个
作者: apricotnz    时间: 2008-3-7 16:56:33

感谢啊~~~~~~~~~~~
作者: luvwei    时间: 2008-3-8 12:18:29

Study 3: A road safety researcher was interested in the effects of alcohol on the driving ability of young adults. A sample of 50 young adults was obtained and each was randomly allocated to either an alcohol group or a no alcohol group. The members of the alcohol group each drank 700ml of beer then did a 10 minute session on a driving simulator. The members of the no alcohol group just did a 10 minute session on a driving simulator. For each member, the driving simulator reported the number of errors made during their 10 minute session.

(d) For study 3, students had differing drinking histories, with some being heavy drinkers, some being moderate drinkers and some being mild drinkers.
Consider the statement: “The two groups of students in study 3 __________ roughly balanced with respect to previous drinking history.”
Which one of the following phrases would best fill in the missing gap in the statement?
“will be” “are likely to be” “are not likely to be” “wont be”
Briefly justify your choice.

他都没有说作出来结果是怎样，要怎么决定？他是不是
ballance

帮帮我吧
作者: 当时的理想    时间: 2008-3-8 14:41:34

我STAT108ASSIGMENT的第1题。。都看得头晕晕的。。。 要怎么算哦 ？？？

谢谢。。。     就是算COURSE WORK的那些东西。。。 很不理解。。
作者: t-multiplier    时间: 2008-3-8 15:10:06

原帖由 luvwei 于 2008-3-8 12:18 发表
Study 3: A road safety researcher was interested in the effects of alcohol on the driving ability of young adults. A sample of 50 young adults was obtained and each was randomly allocated to eith ...


For study 3, students had differing drinking histories, with some beingheavy drinkers, some being moderate drinkers and some being milddrinkers.
Consider the statement: “The two groups of students in study 3__________ roughly balanced with respect to previous drinking history.”
Which one of the following phrases would best fill in the missing gap in the statement?
“will be” “are likely to be” “are not likely to be” “wont be”
Briefly justify your choice.

嗯，这个问题问得很好。你考虑问题里的这点:

Study 3: A road safety researcher was interested in the effects of alcohol on the driving ability of young adults. A sample of 50 young adults was obtained and each was randomly allocated to either an alcohol group or a no alcohol group. The members of the alcohol group each drank 700ml of beer then did a 10 minute session on a driving simulator. The members of the no alcohol group just did a 10 minute session on a driving simulator. For each member, the driving simulator reported the number of errors made during their 10 minute session.

为什么我们要randomly allocate？

因为我们知道所有的驾驶者能分为三种，他们承受酒精的能力不同，这会影响最重的结果。random allocation方法 wishes to achieve a fair and balanced comparison between different groups. 意思是说，随即的取样可以试图得到balanced samples。

如果我们再考虑一下，在统计里，我们能有will be吗？（能有绝对性吗？) 同样，我们能有won't be吗？（绝对不可能）

所以答案应该是？


[ 本帖最后由 t-multiplier 于 2008-3-8 15:19 编辑 ]
作者: t-multiplier    时间: 2008-3-8 15:12:48

原帖由 当时的理想 于 2008-3-8 14:41 发表
我STAT108ASSIGMENT的第1题。。都看得头晕晕的。。。 要怎么算哦 ？？？

谢谢。。。     就是算COURSE WORK的那些东西。。。 很不理解。。


其实这个很简单，就是问你的多少分才可以pass. 你可以参考我在4楼的worked examples.
作者: 当时的理想    时间: 2008-3-8 17:09:06

你的WORK EXAMPLE。。 下载了。。打开为什么是空白的 ？？
作者: 当时的理想    时间: 2008-3-8 20:26:33

为什么打不开你的呢？

还有。。想问 。。ASSIGMENT是怎么计算分数的 ？？  以前高中是你拿到几个A1什么的就可以拿到全部分数。。。  这个ASSIG有40分。。几分及格哦？  是不是像NCEA。。 你答对1半就可以拿到全部分数。。然后分 C .. B..B+那样的呢？？

谢谢 。。

第一题。。我真的不懂怎么算。。。答案是45%？？  第2 小题不知道要怎么EXPLAIN。。。
作者: 当时的理想    时间: 2008-3-8 20:28:19

SELF-SELECTION BIAS。AND THE SELECTION BIAS。。好像大同小异。。我看概念了。。。 可真正区分要犹豫好久。。才能判断出。。  请你讲解下哦 。。 谢谢。。。
作者: z-score    时间: 2008-3-8 21:34:58

原帖由 当时的理想 于 2008-3-8 17:09 发表
你的WORK EXAMPLE。。 下载了。。打开为什么是空白的 ？？


啊？不会吧。我刚才还试了一下，你的电脑有Adobe Reader吧？那个文件是pdf file.
作者: z-score    时间: 2008-3-8 21:43:32

原帖由 当时的理想 于 2008-3-8 20:26 发表
为什么打不开你的呢？

还有。。想问 。。ASSIGMENT是怎么计算分数的 ？？  以前高中是你拿到几个A1什么的就可以拿到全部分数。。。  这个ASSIG有40分。。几分及格哦？  是不是像NCEA。。 你答对1半就可以拿到 ...


奥大的课程和NCEA课程计算分数方法不一样。Assignment的分数会是0到10中间的一个整数。如果你得到37/40，你会被提升到10（满分），如果你得到21/40，你会被提升到6。

第二题他在问你这门课的最终成绩可以怎样计算。你需要把两种不同计算方法都写出来。你明白我说的意思吗？
作者: z-score    时间: 2008-3-8 21:46:38

原帖由 当时的理想 于 2008-3-8 20:28 发表
SELF-SELECTION BIAS。AND THE SELECTION BIAS。。好像大同小异。。我看概念了。。。 可真正区分要犹豫好久。。才能判断出。。  请你讲解下哦 。。 谢谢。。。


Selection bias和self selection bias的最大区别是selection bias是在一个sample里出现，self selection没有一个固定的sample。

Selection bias指的是你的sample与population of interest不一样。

Self selection bias指的是当你没有一个固定的sample下，那些自愿参加调查人所带来的偏差。
作者: ysm860929    时间: 2008-3-9 00:48:45

新生好可爱,这些分怎么算,以后Assignment做多了就知道了
作者: 阴雨天    时间: 2008-3-9 13:10:42

我有一个问题啊:
1.observation studies 和 experiments有什么不同? 请分别给解释一下 谢谢
作者: 阴雨天    时间: 2008-3-9 13:15:45

还有一个问题111
A group of biologists is interested in surveying the abundance of barrel cactus in a particular desert. They divide the desert area up into 1200 equal sized rectangular areas. Of these, 247 areas are too difficult to access, so are excluded. Of the remaining 953 areas, 50 are chosen at random to be surveyed. The biologists then randomly select a 100 square metre section of each of these areas to survey. The number of barrel cacti in each of the chosen sections is then measured.
Briefly describe how you could use a table of random numbers to select 50 out of the 953 areas to survey.

非常感谢!!!
作者: 阴雨天    时间: 2008-3-9 13:50:17

sampling error 和 non-sampling error的解释好象Course book上并没有明确指出 就麻烦LZ了! 谢谢
作者: luvwei    时间: 2008-3-9 16:29:18

谢谢搂住啊
作者: z-score    时间: 2008-3-9 19:07:08

原帖由 阴雨天 于 2008-3-9 13:10 发表
我有一个问题啊:
1.observation studies 和 experiments有什么不同? 请分别给解释一下 谢谢


阿童木现在还没有回家，过一会儿回到家我马上给你解答。

回来了，哦耶。

Experiments可以randomly allocate subjects, 意思是说如果你从新再搞一次试验，在A组的人或东西可以变为B组的人或东西。每次试验，不同组的组合纯属依靠几率。

Observational study的不同组不能改变，举例子: 比较男女或老少。男就是男，不是我们randomly allocate给他的。如果老就是老，不是我们给他的年龄。

[ 本帖最后由 z-score 于 2008-3-9 19:26 编辑 ]
作者: z-score    时间: 2008-3-9 19:28:59

原帖由 阴雨天 于 2008-3-9 13:15 发表
还有一个问题111
A group of biologists is interested in surveying the abundance of barrel cactus in a particular desert. They divide the desert area up into 1200 equal sized rectangular areas. Of ...


你会用course book后面的那个table of random numbers吗？这个问题就是让你解释你能怎样用table of random numbers。

[ 本帖最后由 z-score 于 2008-3-9 19:34 编辑 ]
作者: z-score    时间: 2008-3-9 19:33:38

原帖由 阴雨天 于 2008-3-9 13:50 发表
sampling error 和 non-sampling error的解释好象Course book上并没有明确指出 就麻烦LZ了! 谢谢


这是一个很好的问题。

你来想象一个飞镖与飞镖盘。

假设你扔了4个飞镖，你这4个飞镖的中心与飞镖盘的圆心的距离就是non-sampling error。

你这4个飞镖与这4个飞镖中心的距离就是sampling error。
作者: mayigo    时间: 2008-3-9 22:26:25

A group of biologists is interested in surveying the abundance of barrel cactus in a particular desert. They divide the desert area up into 1200 equal sized rectangular areas. Of these, 247 areas are too difficult to access, so are excluded. Of the remaining 953 areas, 50 are chosen at random to be surveyed. The biologists then randomly select a 100 square metre section of each of these areas to survey. The number of barrel cacti in each of the chosen sections is then measured.
1.is non-response bias a potential problem with the survey?briefly justify your answer.
2.is selection bias a a potential problem ?briefly justify your answer.
请问高手，我可不可以把247 areas 看作是non-response bias ？
而953 areas看作是整个1200areas看作是selection bias
另外如果一个调查有80%人回答和20%人不回答，那那个20%人不回答是non-response bias ，用80%人回答来代表整体是selection bias 吗？到底non-response bias 和selection bias 有什么区别？
作者: z-score    时间: 2008-3-9 22:41:52

原帖由 mayigo 于 2008-3-9 22:26 发表
A group of biologists is interested in surveying the abundance of barrel cactus in a particular desert. They divide the desert area up into 1200 equal sized rectangular areas. Of these, 247 areas ...


”而953 areas看作是整个1200areas看作是selection bias“

恩，这个你说得很对。Those that are too difficult to access may be totally different from the 953 that can be accessed.

"我可不可以把247 areas 看作是non-response bias ？"

他问的这个问题很tricky。Non-response bias是在你take一个sample时候没有得到回复所造成的。在这里，你take的sample size是50，50块土地你都得到了cactus number。所有non-response bias is not present。

Selection bias是difference between your sample and the population of interest。

Non-response bias是在你sample的那些人或东西里没有给你回复所造成的bias。
作者: mayigo    时间: 2008-3-9 22:52:17

原帖由 z-score 于 2008-3-9 22:41 发表


”而953 areas看作是整个1200areas看作是selection bias“

恩，这个你说得很对。Those that are too difficult to access may be totally different from the 953 that can be accessed.

"我可不可以 ...

谢谢，那lz,那如果953 areas是selection bias的话，，最后一个问题问这个是不是sampling errors,而selection bias是non-sampling errors,那这个survery 是否应该是non-sampling erro人?而且我也没有觉得他存在任何behavioural consideration,感觉这个survey 完全不是调查性质的，好像和non-response bias ，behavioural consideration没有任何关系似的，我都糊涂了，

[ 本帖最后由 mayigo 于 2008-3-9 22:54 编辑 ]
作者: z-score    时间: 2008-3-9 23:01:31

原帖由 mayigo 于 2008-3-9 22:52 发表

谢谢，那lz,那如果953 areas是selection bias的话，，最后一个问题问这个是不是sampling errors,而selection bias是non-sampling errors,那这个survery 是否应该是non-sampling erro人?而且我也没有觉得他存在 ...


恩，你不要被出题的人搞糊涂了。

一般不涉及到人类的survey不会有很多non-sampling error, 例如behavioural considerations, non-response bias, self selection bias, question and format effect都不会有。

Sampling error is always present in surveys. Without sampling error we will be doing maths, not stats.
作者: mayigo    时间: 2008-3-9 23:07:19

原帖由 z-score 于 2008-3-9 23:01 发表


恩，你不要被出题的人搞糊涂了。

一般不涉及到人类的survey不会有很多non-sampling error, 例如behavioural considerations, non-response bias, self selection bias, question and format effect都不会 ...

但是LZ不是认为953 AREAS是SELECTION BIAS的吗？那SELECTION BIAS是NON-SAMPLING ERROR（COURSE BOOK ）有说道，那这个SURVEY为什么不是non-sampling error？
作者: z-score    时间: 2008-3-9 23:11:54

原帖由 mayigo 于 2008-3-9 23:07 发表

但是LZ不是认为953 AREAS是SELECTION BIAS的吗？那SELECTION BIAS是NON-SAMPLING ERROR（COURSE BOOK ）有说道，那这个SURVEY为什么不是non-sampling error？


是的，这个survey有selection bias, which is a non-sampling error。还有sampling error。
作者: mayigo    时间: 2008-3-9 23:15:01

原帖由 z-score 于 2008-3-9 23:11 发表


是的，这个survey有non-sampling error。还有sampling error。

谢谢LZ，那就是说一个SURVEY，即可以有non-sampling error 也可以有sampling error
作者: z-score    时间: 2008-3-9 23:20:11

原帖由 mayigo 于 2008-3-9 23:15 发表

谢谢LZ，那就是说一个SURVEY，即可以有non-sampling error 也可以有sampling error


是的，你找到了精髓。任何统计study都会有non-sampling error和sampling error。我们的任务是去减小non-sampling by designing and executing the study more carefully。我们减小sampling error的方法是take a larger sample size。
作者: mayigo    时间: 2008-3-9 23:24:54

原帖由 z-score 于 2008-3-9 23:20 发表


是的，你找到了精髓。任何统计study都会有non-sampling error和sampling error。我们的任务是去减小non-sampling by designing and executing the study more carefully。我们减小sampling error的方法是ta ...

太谢谢LZ
作者: glasszon    时间: 2008-3-10 13:23:40

Come on ATM, where's all the resources for stats326?
作者: mayigo    时间: 2008-3-11 01:55:34

Study 1: A marketing manager for a chain of 64 small bakeries was interested in how different special offers affected sales. 20 of the bakeries were randomly chosen to have a special offer where customers could purchase three loaves of bread for the price of two. 20 of the remaining bakeries were randomly selected to sell loaves of bread with a 20% discount. The remaining bakeries did not offer any discount. After a week, the total number of loaves of bread sold at each bakery was recorded.
Study 2: A university researcher was interested in whether there is a difference, between commerce and arts graduates, in the number of different jobs students went on to work in after graduating. Random samples of 200 commerce and 200 arts graduates were drawn from the graduation lists in 1997. Each graduate was contacted and the number of different jobs they had worked in the 10 years since graduating was recorded.
Study 3: A road safety researcher was interested in the effects of alcohol on the driving ability of young adults. A sample of 50 young adults was obtained and each was randomly allocated to either an alcohol group or a no alcohol group. The members of the alcohol group each drank 700ml of beer then did a 10 minute session on a driving simulator. The members of the no alcohol group just did a 10 minute session on a driving simulator. For each member, the driving simulator reported the number of errors made during their 10 minute session.

Which of the studies, if any, included a control group? For the studies that include one, briefly describe the control group.
Which of the studies, if any, used placebos?
请问楼主，什么是control group，在这3个调查里有control group.
吗？
另外第二个问题怎么看似和题目无关，是不是药物的调查报告才有placebo
作者: z-score    时间: 2008-3-11 08:41:18

原帖由 mayigo 于 2008-3-11 01:55 发表
Study 1: A marketing manager for a chain of 64 small bakeries was interested in how different special offers affected sales. 20 of the bakeries were randomly chosen to have a special offer where  ...


你问了一个很好的问题。

在一个study里，我们可以把不同的group看为treatment group, placebo group和control group。一个study的最终结论是根据treatment group和control group的比较。例如Study 1, 你想知道的是discount对销量有没有影响。这里，你要比较买三送一，打八折和没有discount的店。如果买三送一和打八折店的销量比没有discount的高，那么我们就可以得出结论。

所以，如果在一个study里，你要compare with something, 那么那个something就是control group.

Placebo一般是在于吃药有关的study里。例如，吃药的group是treatment group, 不吃药的是control group, 吃糖药丸的是placebo, 因为人吃任何药都会有心理和生理作用，感觉自我良好(placebo effect).

原帖由 glasszon 于 2008-3-10 13:23 发表
Come on ATM, where's all the resources for stats326?


I don't have any.

[ 本帖最后由 z-score 于 2008-3-11 08:48 编辑 ]
作者: 当时的理想    时间: 2008-3-11 09:18:46

WHat  is your sta10X's work example for?  Is not the answers for ASSIGN 1 ,isn't it ??
  
作者: z-score    时间: 2008-3-11 09:38:58

原帖由 当时的理想 于 2008-3-11 09:18 发表
WHat  is your sta10X's work example for?  Is not the answers for ASSIGN 1 ,isn't it ??
  


Nope, it's not, hehe. It's my own example of how to set out a STATS10x assignment. Hope it helps.

[ 本帖最后由 z-score 于 2008-3-11 10:23 编辑 ]
作者: 阴雨天    时间: 2008-3-11 16:08:07

非常非常感谢LZ~~~ 好人一个
作者: 天外飞猪    时间: 2008-3-12 00:23:55

太谢谢lz了..
我1定要努力跟努力学习
=我做到assign不会还得请教lz呢..
请多多帮忙
作者: mayigo    时间: 2008-3-12 17:28:49

non-response can cause bias in surveys because non-respondents can behave differently from people who respond
请问楼主能解释以下这句话为什么是对的吗？特别是non-respondents can behave differently frompeople who respond 这句话怎么解释，non-respondents 本来就不做回答，为什么能 behave differently frompeople who respond？
作者: z-score    时间: 2008-3-12 21:03:15

原帖由 mayigo 于 2008-3-12 17:28 发表
non-response can cause bias in surveys because non-respondents can behave differently from people who respond
请问楼主能解释以下这句话为什么是对的吗？特别是non-respondents can behave differentl ...


恩，问得很好，这句话概念比较抽象。举一个例子，一个marketing research公司做一个民意调查，这家公司派员工在白天给1000户人家打电话，问他们在08年的大选会选哪个政党。在白天，能在家里休息的很多是退休的老人，他们比较喜欢投优先党。白天在上班的人们比较喜欢投国家党和工党。如果在一个1000人的sample, 只有500个人回答了，而且这500人中很多是老年人，那么这个民意调查的结果就会有non-response, 因为从没在家的500 respondents和500 non-respondents得出的结果会不一样。这就是non-respondents can behave differently from people who do.
作者: mayigo    时间: 2008-3-12 22:51:38

[楼主太强了，回答的正是好，谢谢谢谢谢谢谢谢谢谢谢谢，哦，因为从没在家的500 respondents和500 non-respondents得出的结果会不一样。这就是non-respondents can behave differently from people who do.是不是应该因为从没在家的500 non-respondents和500respondents得出的结果会不一样。这就是non-respondents can behave differently from people who do.



[ 本帖最后由 mayigo 于 2008-3-12 22:53 编辑 ]
作者: 雨中小刀    时间: 2008-3-13 00:30:27

有个问题啊..现在在做208的assignment 1, 第一题,在输入了survey.df<-read.table(file choose(),header=T,选择了文件的路径,从买的光盘里直接到s2008a,再回车以后出现
> library(s20x)
> survey.df<-read.table(file.choose(),header=T)
> attach(survey.df)

        The following object(s) are masked from package:datasets :

         sleep

> survey.df(1:5)
错误: 没有"survey.df"这个函数

数据就显示不出来,是怎么回事啊? 多谢啦...
作者: z-score    时间: 2008-3-13 08:08:01

原帖由 雨中小刀 于 2008-3-13 00:30 发表
有个问题啊..现在在做208的assignment 1, 第一题,在输入了survey.df library(s20x)
> survey.df attach(survey.df)

        The following object(s) are masked from package:datasets :

         slee ...


应该是
> survey.df(1:5, )

你少打了一个逗号。
作者: z-score    时间: 2008-3-13 08:12:24

原帖由 mayigo 于 2008-3-12 22:51 发表
[楼主太强了，回答的正是好，谢谢谢谢谢谢谢谢谢谢谢谢，哦，因为从没在家的500 respondents和500 non-respondents得出的结果会不一样。这就是non-respondents can behave differently from people who do.是不 ...


对的，现在你彻底理解了。
作者: spirithell    时间: 2008-3-13 19:29:18

Question 3. [12 marks] [Chapter 1]
Consider the following studies:
Study 1: A marketing manager for a chain of 64 small bakeries was interested in how different special offers affected sales. 20 of the bakeries were randomly chosen to have a special offer where customers could purchase three loaves of bread for the price of two. 20 of the remaining bakeries were randomly selected to sell loaves of bread with a 20% discount. The remaining bakeries did not offer any discount. After a week, the total number of loaves of bread sold at each bakery was recorded.
Study 2: A university researcher was interested in whether there is a difference, between commerce and arts graduates, in the number of different jobs students went on to work in after graduating. Random samples of 200 commerce and 200 arts graduates were drawn from the graduation lists in 1997. Each graduate was contacted and the number of different jobs they had worked in the 10 years since graduating was recorded.
Study 3: A road safety researcher was interested in the effects of alcohol on the driving ability of young adults. A sample of 50 young adults was obtained and each was randomly allocated to either an alcohol group or a no alcohol group. The members of the alcohol group each drank 700ml of beer then did a 10 minute session on a driving simulator. The members of the no alcohol group just did a 10 minute session on a driving simulator. For each member, the driving simulator reported the number of errors made during their 10 minute session.

(c) For the studies that are observational, could an experiment have been easily carried out instead? If so, briefly explain how. If not, briefly explain why not.
stuay 1 is experiment,这个就不讨论了。
study 2 虽然是observational reasearch,但是好像可以搞成experiment，请问怎么下手呢？
study 3 好像没法搞成experiment.
以上是我对Q3--(C) 的看法，请您帮我看看，怎么做这一题？谢谢谢谢。！~~~~

我现在就Q3和Q5不会做，唔唔唔唔唔唔~~~~一点点地问，谢谢阿童木。
作者: spirithell    时间: 2008-3-13 19:36:19

还是Q3， (d)已经看过上面的帖子了，
(e) It was later suggested that gender could be a significant factor in Study 3. How could the study design be modified to take into account the gender effect?能不能帮忙提示一下？
(f) Which of the studies, if any, included a control group? For the studies that include one, briefly describe the control group。 应该是study 3,自己胡编一下就行了。
(h) Could the results of a study such as Study 2 be used to argue that any overall difference in the number of different jobs held is due to the degree studied? Briefly justify your answer.实在是不明白，怎么还可以argue捏，晕晕滴说， ，不好意识，实在太笨了。
作者: spirithell    时间: 2008-3-13 19:39:00

Statistics Assistance Room

Assistance room tutors provide one-on-one help with work in lectures, assignments, and with test & exam preparation. You can also ask for help with the calculator worksheet.

When: Staffed from 9am – 4pm, Monday – Friday.

Where: Room B09, Basement of Building 303, Science Centre.
作者: 当时的理想    时间: 2008-3-13 21:18:57

  LZ。。那些概念是理解了。。可是语言不知道怎么组织哦。。  就是无处下手。。知识点是懂了 。。。 只怪英语不那么好。。怎么办哦？

还有。。 USE THE TABLE OF RANDOM NUMBERS。。 那个不知道要怎么表达哦、、、 老师课上讲用自己手机号码的后2个数字来选一组号码出来。。。 ASSIG的题目也要那样吗？ 还是自己随便选哦 ？？？？

谢谢。。。。
作者: z-score    时间: 2008-3-13 21:33:35

study 2 虽然是observational reasearch,但是好像可以搞成experiment，请问怎么下手呢？

如果study 2变成experiment的话，学生们会被randomly allocated into the commerce or art faculty. 你觉得这样可能吗？可能强制一个人去读BCom或BA?

study 3 好像没法搞成experiment.

study 3 ms是experiment哦。你看这句话was randomly allocated to either an alcohol group or a no alcohol group。

我现在就Q3和Q5不会做，唔唔唔唔唔唔~~~~一点点地问，谢谢阿童木。

Q5可以参考4楼past assignment的答案。

[ 本帖最后由 z-score 于 2008-3-13 21:50 编辑 ]
作者: z-score    时间: 2008-3-13 22:44:16

原帖由 当时的理想 于 2008-3-13 21:18 发表
  LZ。。那些概念是理解了。。可是语言不知道怎么组织哦。。  就是无处下手。。知识点是懂了 。。。 只怪英语不那么好。。怎么办哦？

还有。。 USE THE TABLE OF RANDOM NUMBERS。。 那个不知道要怎么表 ...


哦，如果你怕自己的英文表达能力不好没事。你先写出来，我帮你改。如果你不想让别人看到你写的，你发给我PM也可以。

其实答案不用说很多，写一些简单的解释就好了。

[ 本帖最后由 z-score 于 2008-3-13 22:50 编辑 ]
作者: z-score    时间: 2008-3-13 22:48:45

原帖由 spirithell 于 2008-3-13 19:36 发表
还是Q3， (d)已经看过上面的帖子了，
(e) It was later suggested that gender could be a significant factor in Study 3. How could the study design be modified to take into account the gender effect? ...


(e) It was later suggested that gender could be a significant factor inStudy 3. How could the study design be modified to take into accountthe gender effect?能不能帮忙提示一下？

Q3 e) 很大的一个hint, blocking是什么东西？Blocking能在study 3用吗？

(h) Could the results of a study such as Study 2 be used to argue thatany overall difference in the number of different jobs held is due tothe degree studied? Briefly justify your answer.

A study can argue that any overall difference is due to the treatment group of the study if and only the study is a well designed and executed experiment. If the study is an observational study, then we cannot make such causation statements.
作者: 303B25    时间: 2008-3-14 10:30:13     标题: STATS 210

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作者: z-score    时间: 2008-3-14 10:55:17

原帖由 303B25 于 2008-3-14 10:30 发表
Question: For questions asking whether certain events form a partition, what's the best way to explain it? I usually answer by stating whether all the probabilities add up to one and whether they ...


Hi, yeah what you said is perfectly fine. Now, have you had a look at my past assignment resources? In there you can find the full written explanation to your question.
作者: 303B25    时间: 2008-3-14 11:09:12

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作者: z-score    时间: 2008-3-14 11:13:31

原帖由 303B25 于 2008-3-14 11:09 发表


I just looked at that, neat hand writing. Thanks a lot, I'll have a look tonight when I have more time. :'( Accounting assignment due in 50 mins.


Thank you, good luck with the accounting assignment.
作者: qian.qian    时间: 2008-3-14 20:48:00     标题: stats210 ASSIGNMENT 1

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作者: 303B25    时间: 2008-3-14 21:39:40     标题: 回复 #68 qian.qian 的帖子

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作者: z-score    时间: 2008-3-14 21:49:05

原帖由 qian.qian 于 2008-3-14 20:48 发表
1. Jenny is planning to go tramping next weekend. The weather forecast indicates that there is a 40%
chance of rain, a 50% chance of wind and a 30% chance that there will be rain and wind. The s ...


恩，你说得很对，很聪明。

To 303B25, yep both of you guys got it right.
作者: 落水    时间: 2008-3-15 22:38:52

LZ是个大好人啊～～～～～～～～～～～～
作者: 水鱼皇后    时间: 2008-3-16 07:39:32

One of the main tourism sites in Wellington is the cable car. The lower station is just off the main
street and it is a quick ride up to the Kelburn station at the top of the hill. At the top are some
stunning views all over Wellington (if the notorious local weather is permitting). There is also a small
lunch bar, a restaurant, a new cable car museum and access to the Botanic Gardens. The Cable Car is
very popular with tourists as it is centrally located, offers great views and is relatively quick. When
cruise ships stop in Wellington for the usual one-day stay, there are often queues, even outside the
usual commuter rush hours.
The City Council’s tourism office is very interested in what tourists think of this major tourism
experience. As a result they employed a student to do a very quick interview with a minimum of 200
people at the area at the top of the Cable Car. The student had to do the work in the week before
Christmas. In addition, the tourism office installed a touch-screen survey computer at the back of the
cable car museum. The survey on the computer took about 5 minutes and asked questions in English.

What are the likely problems with sampling in the first approach?
感觉到不对 可是具体是什么又说不出 in the week before xmas 这里有问题吧？可以给点hint吗？
作者: 303B25    时间: 2008-3-16 10:13:37     标题: 回复 #72 水鱼皇后 的帖子

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作者: chanel    时间: 2008-3-16 10:40:15

很好很好~~~~~~太有帮助了
作者: luvwei    时间: 2008-3-16 13:16:56

原帖由 mayigo 于 2008-3-11 01:55 发表
Study 1: A marketing manager for a chain of 64 small bakeries was interested in how different special offers affected sales. 20 of the bakeries were randomly chosen to have a special offer where  ...



所以楼主

是不是这三个都没有placebo???
作者: z-score    时间: 2008-3-16 13:51:29

原帖由 luvwei 于 2008-3-16 13:16 发表



所以楼主

是不是这三个都没有placebo???


是的，你说得很对。
作者: luvwei    时间: 2008-3-16 14:02:15     标题: ???

???????????????
作者: z-score    时间: 2008-3-16 14:02:44

原帖由 luvwei 于 2008-3-16 14:02 发表
???????????????


这三个study都没有placebo.
作者: luvwei    时间: 2008-3-16 14:03:29

我做了一个box plot

他的形状就是一个很正常的形状

我要怎么comment on it
作者: luvwei    时间: 2008-3-16 14:09:12

作者: z-score    时间: 2008-3-16 14:10:38

原帖由 luvwei 于 2008-3-16 14:03 发表
我做了一个box plot

他的形状就是一个很正常的形状

我要怎么comment on it


你要comment他的median, distribution(left skewed or right skewed, or symmetric), 最后他有一个trick, 就是实际上boxplot看不出来data有一个很大的gap, 你从stem and leaf plot能看出来。
作者: z-score    时间: 2008-3-16 14:11:46

原帖由 luvwei 于 2008-3-16 14:09 发表


Sorry, 我比较慢，你看一下我的worked examples, 里面答案会有帮助。
作者: luvwei    时间: 2008-3-16 14:40:13

第五题的那个表格阿

最后打出来的东西最后要包括什么呢？？

因为他说redraw...and bla bla

我print出来的table只有 page number, word lengh , word density

and mean word length at the end..

is that right???


or i need to print out the whole table wif everything in it????


thank you thank you
作者: z-score    时间: 2008-3-16 15:25:35

原帖由 luvwei 于 2008-3-16 14:40 发表
第五题的那个表格阿

最后打出来的东西最后要包括什么呢？？

因为他说redraw...and bla bla

我print出来的table只有 page number, word lengh , word density

and mean word length at the end..

...


你到4楼里面找一下去年的Assignment 1答案。那里的表格就是你第五题所需要的表格。
作者: qian.qian    时间: 2008-3-16 16:10:48     标题: stats 210 A1 Q3

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作者: qian.qian    时间: 2008-3-16 16:32:54

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作者: 303B25    时间: 2008-3-16 20:00:22     标题: 回复 #85 qian.qian 的帖子

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作者: 303B25    时间: 2008-3-16 20:03:25     标题: 回复 #86 qian.qian 的帖子

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作者: ztswyz    时间: 2008-3-17 08:38:35

999999一道书上的例题 atom 帮忙啊


我怎么连书上的例题都不会了呢

这是一个stat题
貌似可以用r程序做

Q1

H0：u＝35
n= 25
mean= 37.77
sd=3.66
se=0.732


用r可以算出
p-value=0.0008996

哪个大虾告诉我这个r是怎么算得...

Q2


顺便问一下 如果已知95％ confidence interval 得出 83.75 ,84.24
如何反算...
或算 83 的p-value
作者: z-score    时间: 2008-3-17 08:39:09

不好意思，阿童木周末有点忙，今天上午我会解答从72楼到89楼的所有问题。

请稍等，谢谢支持。


更新：

所有问题已经回答完毕。

[ 本帖最后由 z-score 于 2008-3-17 10:48 编辑 ]
作者: z-score    时间: 2008-3-17 10:29:59

原帖由 水鱼皇后 于 2008-3-16 07:39 发表
One of the main tourism sites in Wellington is the cable car. The lower station is just off the main
street and it is a quick ride up to the Kelburn station at the top of the hill. At the top ar ...

原帖由 303B25 于 2008-3-16 10:13 发表
1) The people traveling during the week before Christmas might behavedifferently to people not traveling during that time. (Consider mostpeople travel between Christmas and New Years, retail wo ...


Thank you 303B25.

Addional to 303B25's response, this survey has a lot of non-response bias, like the people who can't understand English might refuse to do the interview completely.

If the day has very bad weather, not a lot of people will come up to the top of the mountain to start with.

This survey may have interviewer effect as the survey could be done using a computer or through an interviewer.

Hope this helps.
作者: z-score    时间: 2008-3-17 10:37:51

原帖由 ztswyz 于 2008-3-17 08:38 发表
999999一道书上的例题 atom 帮忙啊


我怎么连书上的例题都不会了呢

这是一个stat题
貌似可以用r程序做

Q1

H0：u＝35
n= 25
mean= 37.77
sd=3.66
se=0.732


用r可以算出
p-value=0.000 ...


Q1 R code

test.statistic <- (37.77-35)/(3.66/sqrt(25))
2*(1-pt(abs(test.statistic),25-1))

Hope this works!

Q2

没太看懂，反算什么东西？那个confidence interval的P-value?
作者: z-score    时间: 2008-3-17 10:42:15

原帖由 qian.qian 于 2008-3-16 16:10 发表

下面这两句话应该怎么写啊...
"None of the cars with dodgy steering wheels are missing both windows and passenger
seats. The cars without steering wheels fortunately have both wi ...


None of the cars with dodgy steering wheels are missing both windows and passenger seats.

IP(W AND P|D) = 0
作者: z-score    时间: 2008-3-17 10:46:42

原帖由 qian.qian 于 2008-3-16 16:32 发表
3. Basement Rentals is a dubious car rental outfit based in Auckland. Prices are cheap, but so is the
quality of the rental cars! Each car either has a reasonable steering wheel, a dodgy steerin ...


嗯，意思就是这个，但是解释怎样写出来你可以参考我的past assignment answers, 那种写法老师会接受.

希望能有帮助．
作者: poison_ivy    时间: 2008-3-17 19:43:12

341的问题...
a local surf life saving club wants to replace its 30 year old clubrooms which are dilapidated and too small for the number of club members and all the services the club provides.the club is located on a public reserve,right on the beach in the middle of a wealthy beach suburb.the local shopping centre,just 20 metres away down the road,is a busy local hub with a supermarket,a selection of shops and lots of cafes and restaurants.as part of the development the club management has suggested putting in a cafe.the local Council has suggested that before the club gets to far in planning or design of the new clubrooms,it should conduct some research to see what people think about the proposal for a new club--especially people who could be affected by a new larger club which is offering new services. the Council indicates that the results of theis research will be important in determining whether the Council will support the development of new larger clubrooms on public land.

the club managment ask for help in designing a survey of people who could be affected by the development of a new larger club.

偶只想到club members是一个populations of  interest.....还有哪些可以是populations of interest捏.....？

后面还问what could be use as sampling frame and how it would be used......
.....无知的某人完全晕了...|||||||||.....毫无概念....

请求搂主帮忙 谢谢~~

[ 本帖最后由 poison_ivy 于 2008-3-17 19:48 编辑 ]
作者: qian.qian    时间: 2008-3-17 20:15:53     标题: stats210

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作者: 303B25    时间: 2008-3-17 20:30:15     标题: 回复 #96 qian.qian 的帖子

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作者: ztswyz    时间: 2008-3-17 21:31:09     标题: 回复 #92 z-score 的帖子

> test.statistic <- (37.77-35)/(3.66/sqrt(25))
> 2*(1-pt(abs(test.statistic),25-1))
[1] 0.0009074216
>
不对啊 应该是
p-value=0.0008996
先不管第二题了 过几天答案下来了再问...
先问第一题
作者: z-score    时间: 2008-3-17 21:40:26

原帖由 ztswyz 于 2008-3-17 21:31 发表
> test.statistic  2*(1-pt(abs(test.statistic),25-1))
[1] 0.0009074216
>
不对啊 应该是
p-value=0.0008996
先不管第二题了 过几天答案下来了再问...
先问第一题


0.0009074216和0.0008996你看才差多少，我这个是拿R算的，你给的那个是不是用SPSS或Excel这种软件算得啊？不同软件算出来的P-value会不一样。
作者: z-score    时间: 2008-3-17 22:06:19

原帖由 303B25 于 2008-3-17 20:30 发表
Should be IP((W union P) given M)
that's what I think, not exactly sure though
are you in the 8am lecture?

原帖由 qian.qian 于 2008-3-17 20:15 发表
The cars without steering wheels fortunately have both windows and passenger seats present.

应该是IP(W and P given M)=0
还是IP((complement of W and P) given M)=1


应该是IP((W & P)` | M)=1.

To 303B25: I think she is right.

The cars without steering wheels fortunately have both windows and passenger seats present.

This is saying given the car is without a steering wheel, |W, the probability both (intersection) (P&W)`
作者: z-score    时间: 2008-3-17 22:07:49

原帖由 poison_ivy 于 2008-3-17 19:43 发表
341的问题...
a local surf life saving club wants to replace its 30 year old clubrooms which are dilapidated and too small for the number of club members and all the services the club provides.th ...


不好意思啊，341的问题好长，我先看完在解答。
作者: 水鱼皇后    时间: 2008-3-17 22:41:50

原帖由 z-score 于 2008-3-17 10:29 发表




Thank you 303B25.

Addional to 303B25's response, this survey has a lot of non-response bias, like the people who can't understand English might refuse to do the interview completely.
...



谢谢303B25 & atm的回答
还有一个问题 也是这个题目的

After your comments, the Council decides to focus solely on cruise ship visitors. They
want to know what proportion of them visit the Cable Car and what they think of the
experience. What sampling frame could be used to generate a representative sample for
this survey and how would you use it?

这里的sampling frame是什么 我们不能access a list吧？
如果random sample cruise的乘客的话 这样算是sampling frame吗？

[ 本帖最后由 水鱼皇后 于 2008-3-17 22:46 编辑 ]
作者: z-score    时间: 2008-3-18 09:14:32

原帖由 水鱼皇后 于 2008-3-17 22:41 发表



谢谢303B25 & atm的回答
还有一个问题 也是这个题目的

After your comments, the Council decides to focus solely on cruise ship visitors. They
want to know what proportion of them visi ...


嗯，sampling frame for cruise ship visitors可以看为所有从Wellington港口下船的游客．你可以让工作人员在Wellington港口等待油轮靠港，randomly sample所有下船的游客们．
作者: z-score    时间: 2008-3-18 09:23:12

原帖由 poison_ivy 于 2008-3-17 19:43 发表
341的问题...
a local surf life saving club wants to replace its 30 year old clubrooms which are dilapidated and too small for the number of club members and all the services the club provides.th ...


Population of interest应该包括所有会受到new club room影响的人们．

The local shopping centre, just 20 metres away down the road, is a busylocal hub with a supermarket, a selection of shops and lots of cafes andrestaurants. As part of the development the club management hassuggested putting in a cafe.

population of interest(我想)应该是所有去超市，咖啡店和餐馆的人们．

sampling frame(我想)可以是在所有surrounding suburbs的人们．



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