Help with Search
 
 
Picture of Martin Kessler
Polling Puzzles
by Martin Kessler - Sunday, January 13, 2008, 12:45 PM
 

Is the margin of error equal to two standard deviation?

For example in problem one is the standard deviation .01 because the margin of error is 2%?

And after that do I use the formula and solve for n?

Picture of Doug McG
Re: Polling Puzzles
by Doug McG - Sunday, January 13, 2008, 10:09 PM
 
Yup (if the confidence level is 95%).

Yes.

Uh huh.
Picture of Hannah Sears
Re: Polling Puzzles
by Hannah Sears - Sunday, January 13, 2008, 09:42 PM
 
what about with a 97% confidence level? then its not 2 standard deviations, is it? do u just have to find the z for 97%?
and also how do u find confidence level? basically im having trouble with #2 and #4.
Picture of Doug McG
Re: Polling Puzzles
by Doug McG - Sunday, January 13, 2008, 09:44 PM
 
Yup.

I really like these self-answering questions.
Picture of Hannah Sears
Re: Polling Puzzles
by Hannah Sears - Sunday, January 13, 2008, 09:43 PM
 
how do u find the z tho? i dont remember how to interpolate that direction

Picture of Doug McG
Re: Polling Puzzles
by Doug McG - Sunday, January 13, 2008, 10:07 PM
 
Well, the interpolation is done pretty much the same way. You know from the table that z is between 2.1 and 2.2 (closer to 2.2). What percent of the way between .9643 and .9722 is .97? Go that percent of the way between 2.1 and 2.2.
Picture of Doug McG
Re: Polling Puzzles
by Doug McG - Sunday, January 13, 2008, 10:05 PM
 
Remember, the margin of error is half of the confidence interval.

The confidence level is related to the z-value (number of standard deviations) through the chart on pg 399.

And the standard deviation is related to the size of the poll through the formulas we discussed in class (assuming p = .5).
Skip Navigation

Navigation