Empirical evidence
The term empirical evidence is used to define the information acquired by experimentation and/or observation. Researchers record and analyze this acquired data. This is the process that forms the central part of the scientific method. Determining the optimal Sample size for a study assures an adequate power to detect statistical significance. Hence it is a critical step in the design of planned research protocol. Using too many participants in a study can be expensive as well as exposes more number of subjects to the procedure. Again, if the study is under powered, it would statistically be inconclusive and may make the whole protocol a failure. Before beginning with the collection of any pieces of empirical data, the scientists skillfully design their research methodology to predict the accuracy, the quality of the data and integrity of the data. Depending upon the purpose of investigation, types of variables and conditions in which the research is conducted.