Abstract
The z-test and t-test have been applied for testing the hypothesis that the population mean is equal to the specified mean value. In this paper, we will introduce the modification of the z-test and t-test using the double sampling scheme. We will present the operational process to implement the proposed tests. The power of the proposed test will be calculated for normal distribution, the Weibull distribution, Chi-square distribution, t-distribution and Cauchy distribution for various sample sizes. The application of the proposed tests is given using the speed of earth data. From the comparisons, it is found that the proposed test provides a higher power of the test for all distributions than the existing z-test.