Usually, determining the sample size requires an error rate you can accept and
a selected confidence level. In many types of studies the knowledge of the
variance is helpful. There are tables in many standard texts which can give
you the necessary n for your poll. With a 70-30 break, I would estimate you
will need about 800 or so. You can also use the little formula below to get a
better picture of the size you might need:
n= Z^2 pq/E^2 where Z = square of the C.I. in standard error units; p=est.
proportion "for" something; q=est. proportion "against" something; E = sq. of
maximum allowance for error between the actual prop. and the sample prop.
Generally, the greater the n, the lower the standard error of the proportion.
In article <[EMAIL PROTECTED]>,
[EMAIL PROTECTED] (KazakOR) wrote:
>The city in which I live has a population of 126,635. I wish to sample this
>city and generate poll results with a margin of error of 3.5%. How many people
>must I contact to arrive at this confidence level?
>
>Thanks for any help! BTW, this is not homework; I'm 38 and am arguing with my
>statistics major wife who is probably right in the first place.
>
>Kazak
>Kazak
>"Envy may be one of the seven deadly sins in theological circles, but it is a
>box office winner in every sort of ordinary conversation."
>-William A. Henry III
>"In Defense of Elitism"
