# Calculate confidence interval, Sample Size Estimation for Proportion.

Sample Qnt 561 Confidence Interval Calculate confidence interval

Confidence interval – A confidence interval refers to a set of numbers that are likely contain the population parameter. This is used to calculate the population average or proportion using a sample statistic and an associated level confidence. Here is the formula to calculate a confidence interval (or population proportion) p.

CI = p ± z*sqrt(p*(1-p)/n)
where n is the sample size and z the critical value of the normal distribution standard (Z-score).

Proportion estimation using sample size: This involves the calculation of the needed sample size so that it is possible to accurately estimate an unknown proportion. This requires that you consider the following factors: the desired level of accuracy, the acceptable margin of error, and the assumed value p (the population percentage). If all variables are set, larger sample sizes will yield more accurate estimates. This formula is used to determine the size of required samples given all these variables:

n = [(z^2)*p*(1-p)]//e2 Where z is the critical Z score based on your level of significance (often 95%) and where e is your maximum allowable margin of error.