There are several measures of disease frequency that are used in the epidemiological and medical literature. A perfect diagnostic test would always identify patients as positive if they have the disease and would always be negative in patients without a disease. Descriptive statistics are used to summarise and describe distributions of data. While traditional methods use a test and/or a diagnostic tool to predict a disease state and/or outcome, as discussed at the beginning of this chapter, predictive analysis is becoming increasingly popular due to the emergence of sophisticated data science. When performing research, consulting with a biostatistician is paramount to ensure that the study is designed in a way that facilitates proper analysis. However, having knowledge of the concepts in biostatistics ensures that the clinical goals of the study meet the study design and the analytical plan.