Sampling Distribution: Impact of the Population Reliability on the Sample Size Determination

One of the spiniest problems in the elementary theory of the sampling is the determination of the size of the sample. Several authors tried to answer this question. In this paper, we present the methods of determination of the sample size in order to estimate to a given precision the   population mean, the variance of the population being known or unknown. In the same way, we present the methods of determination of the size of the sample in order to estimate to a given precision the frequency of a character in the population at different level of its reliability denoted here by.the method uses the sampling error of the distribution of the specified statistic.  Notice that the bigger the population reliability (or 100%), the smaller is the necessary sample size to get the best estimation of the parameter. The representativeness of the population doesn't essentially depend on the size of the sample; the size of the sample influences the precision of the measures; to achieve a highest accuracy, it is necessary to increase the sample size. The results of this research will help in determining the sample size to be drawn from different populations (finite or finite).