Calculate Sample Size Population Proportion. Inputs are the assumed or estimated value for the proportion the desired level of confidence the desired precision of the estimate and the size of the population for limited population sizes. Population Sample Size n Z 2 x P 1 - P e 2 Where Z Z Score of Confidence Level P Expected Proportion e Desired Precision N Population Size For small populations n can be adjusted so that n adj Nxn Nn.
Q 1 p 1 0842 0158 Since CL 095 then α 1 CL 1 095 005 α 0025. N is the sample size z is the z-score associated with a level of confidence p is the sample proportion expressed as a decimal. So the formula for obtaining the required sample size is obtained by taking the above equation and solving for n.
We will say that there are 1000 people in the population.
N NX X N 1 where X Z α22 p 1-p MOE 2 and Z α2 is the critical value of the Normal distribution at α2 eg. Its equation can be derived by using population size the critical value of the normal distribution sample proportion and margin of error. Where the population is unknown the sample size can be derived by computing the minimum sample size required for accuracy in estimating proportions. We will say that there are 1000 people in the population.
