This book takes a full study on three estimators namely Simple random sampling without replacement (SRSWOR), double sampling for ratio and double sampling for regression estimators. These estimation procedures were applied to online software repository data obtained on www.download.com and www.sourceforge.net, hence, revealing the undiscovered but important application of Statistics to the improvement of software design and usage. Furthermore, primary data on household were collected with questionnaires which were administered by the staff and students of Nursing School of University College Hospital (UCH) in Nigeria. Empirical analysis was executed in studying the performances of these estimators in estimating the population mean. It was observed that double sampling with regression type estimator claims superiority over other estimators by possessing a minimum optimum variance under certain conditions. Relative efficiency and Coefficient of variation further confirmed this superiority of double sampling for regression with highest efficiency and precision respectively over double sampling for ratio and SRSWOR estimators.