For a sample size n of 100 visitors to Safalra.com, user-agent strings submitted by their browsers showed that 52% of the visitors were using Gecko based browsers such as Mozilla FireFox. Find the 95% confidence interval for the population proportion P for users of Gecko based browsers who visit Safalra.com.
Formulas are written for OpenOffice.org Calc. Replace semi-colons with commas for Excel.
|Confidence interval statistics for proportions|
|Statistic or Parameter||Symbol||Equations||OpenOffice|
|Number of successes or desired results in a sample||r|
|Proportion of successes or desired result in a sample||p||r ÷ n||=r/n|
|Proportion of non-successes, not the desired, or alternate result in a sample||q||1 − p||=1-p|
|Standard error of a proportion p||σp||=SQRT(p*q/n)|
|Margin of error E for a proportion p||E||=TINV(1-c;n-1)*SQRT(p*q/n)|
|Calculate a confidence interval for a population proportion P from the sample proportion p and the margin of error E for the mean.||p − E ≤ P ≤ p + E|