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?

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.