Reference no: EM132401507

a) A Gallup Poll asked the question How would you rate the overall quality of the environment in this country today - as excellent, good, only fair, or poor? In all, 46% of the sample rated the environment as good or excellent. Gallup announced the poll's margin of error for 95% confidence as ± 3 percentage points. Which of the following sources of error are included in the margin of error?

A. The poll dialed telephone numbers at random and so missed all people without phones.  

B. There is chance variation in the random selection of telephone numbers. 

C. Nonresponse - some people whose numbers were chosen never answered the phone in several calls or answered but refused to participate in the poll.

D. All of the above.

(b) What is significance good for? Which of the following questions does a test of significance answer? 

A. Is the observed effect important? 

B. Is the observed effect due to chance?  

C. Is the sample or experiment properly designed? 

D. All of the above.

(c) How much do you plan to spend for gifts this holiday season? An interviewer asks this question of 250 customers at a large shopping mall. The distribution of individual responses is skewed, but the sample mean and standard deviation of the responses are xbar= 437 dollars and s = 65 dollars. Which of the following are true? 

A. If we calculate a confidence interval, it cannot be trusted since the sample responses may be badly biased. 

B. The margin of error for a 95% confidence interval will be less than the margin of error for a 99% confidence interval.

C. The Central Limit Theorem informs us that we can act as if xbar is approximately Normally distributed. 

D. All of the above.