This chapter is dedicated mainly to laboratory professionals who need to design tests starting with sample size considerations and power. It provides multiple examples of calculatng sample size and power in circumstances of varying disease prevalence, varying confidence intervals, varying levels of power, and for different test indices. There may be instances when some of these techniques are used by epidemiologists and clinicians, especially in situations when they must evaluate diagnostic tests before implementing testing in the field. The sensitivity, specificity, and positive and negative predictive value would be indices of interest to both laboratory and clinical professionals. The chapter also gets into concepts that explain differences in commonly used terms such as precision vs. reproducibility, validity vs. reliability, inter-lot variation vs. intra-lot variation. For those in the drug development industry, the concepts of pharmacodynamics and pharmacokinetics are also described. Calculations of the coefficient of variation are included.