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 | |||
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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 |