







Confidence level 
20071119 

From Fara: It is common for public opinion polls to have a " confidence level" of 95%, meaning
that there is a 0.95 probability that the poll results are accurate within the claimed margins of error.
If six different organizations conduct independent polls, what is the probability that all
six of them are accurate within the claimed margins of error? Does the results suggest that
with a confidence level of 95%, we can expect that almost all polls will be within the claimed
margin of error? Answered by Harley Weston. 





Find the sample size needed 
20070513 

From Mini: Find the sample size needed to be 98% confident thata marketing survey on the proportion of shoppers who use the internet for holiday shopping is accurate within a margin of error of 0.02. Assume that the conditions for a binomial distribution are met, and that a current estimate for a sample proportion does not exist. Answered by Penny Nom. 





Margin of error 
20010713 

From Jim: If a survey was completed by four different groups of people as indicated below what would the overall margin of error be for this survey given the fact that the number of people in each group were different?
Group # polled Margin of error
A. 779 +/ 4%
B. 315 +/ 7%
C. 323 +/ 6%
D. 254 +/ 9%
Answered by Andrei Volodin. 

