Design process is fundamental to evidence obtained from biomedical and clinical research, since errors in sampling may adversely affect the evidence derived from the sample. Designs may be classified in several ways, including descriptive versus inferential and experimental versus nonexperimental. While a descriptive study design characterizes samples with respect to independent and outcome variables without any attempt at generalization to the population of interest, inferential studies test specific hypotheses in order to draw inferences on the population, implying those patients who were not studied with the sample.