Question

2. The National polling organization conducted a phone survey of 850 American adults on what they considered to be the most serious problem facing nation’s public schools; 30% said violence. This sample percent is an estimate of the percent of all adults who think that violence is the school’s most serious problem. At 95% level, what is your range of confidence on the percentage of the entire population that considers the violence as the most serious problem in public schools?

Answer 1

Try using a binomial proportion CI formula:

CI95 = p + or - 1.96(√pq/n)
...where p = proportion in the problem, q = 1 - p, n = sample size, √ = square root, and + or - 1.96 represents 95% CI using a z-table.

Your data:
p = .3
q = .7
n = 850

Substitute values into the formula and determine the confidence interval.