Determining Sample Size for Estimating poportions

It is  necessary  to determining  the sample size for a  problem involving  proportions. This deals  with the percentage of frequency  of occurrence. The standard  deviation is  computed considering  the  proportions of  the happening  of the  particular  event. If the  frequency of occurrence is  known  as p and the frequency  of non occurrence is known  as 1 , the  standard deviation  of the  proportion maybe

                   p = √p q/n

The samples  size is determine  as discussed  earlier. The precision and population size have been  the deciding  factors for  determining  the sample size. The precision can again  be expressed absolutely or  relatively. Absolute  precision involves  that the  estimate will be within  plus  or minus  of the true value i ,e,± 5 percentage  points  of the true  value. If  the sample  elements  are selected independently  and if  the sample  size is small the correct  distribution  of the sample proportion will  be binomial. It is  convenient  to employ the normal  approximation for  estimating the  sample size. After the sample  is  drawn and the  sample  promotion  determined  the researcher  determines  the confidence  interval.