T O P I C R E V I E W 
Danny09 
Posted  12/01/2011 : 17:51:00 Hello all! I have a few quick question regarding confidence intervals/margin of error.
1.) Suppose that 518 of the 1,493 respondents for a survey agree with a question. What is the margin of error for the 95% confidence interval?
2.) A study surveyed 2,829 randomly selected 13 to 19yearolds. Of those teenagers, 78% had a television in their room. What is the upper bound on the 95% confidence interval for the proportion of all teens who have a TV set in their room?
I know in both problems you use the formula for finding the square root of a discrete probability model, or S=p(1  p)n
Where p= the same proportion and n= the poulation total
So for question two, p=0.78 and n=2,829
Could anyone help point me in the right direction as to where I go from here? Thanks very much in advance! 
3 L A T E S T R E P L I E S (Newest First) 
Danny09 
Posted  12/02/2011 : 16:37:24 Sorry for the double post, but for problem #2 where p=.78 and n=2,289
I calculated the standard dev. as S = 2.462
This seems somewhat more believable than what I got for #1. 
Danny09 
Posted  12/02/2011 : 16:33:11 quote: Originally posted by royhaas
The margin of error can be defined as onehalf the width of the confidence interval.
Thanks for the reply! I seem to be stuck on calculating the confidence interval though...
For question #1, if the population proportion = 0.347 and N = 1494,
I calculated S = 0.0001511768
Surely this cant be right...? Am I imputing the data into the formula wrong?

royhaas 
Posted  12/02/2011 : 08:09:32 The margin of error can be defined as onehalf the width of the confidence interval. 

