Statistical tests such as the Chi-Square test and Fisher's Exact test are commonly used in research to determine if there is a significant association or difference between two variables. They can be used to compare groups, survey populations, assess response bias, and more. Negative studies, where the p-value is not significant, are also important and should still be published. A case series is a detailed report of a group of subjects who are all experiencing the same outcome. It is typically used for rare or novel diseases and can offer insight into potential links between outcomes and exposures or interventions. Some limitations of case series include the lack of a control group and the difficulty in establishing causal relationships. However, they are inexpensive and can lead to the discovery of new diseases and treatments. Two statistical tests, Fisher's exact test and Pearson's chi squared, are often used in case studies.