Clinicians' guide to statistics for medical practice and research: part I

There are many reasons for inconsistencies (good day, bad day, etc.), but they all boil down to variance. Because in clinical research we rely on a sample of the patient population, variance is a key consideration in the evaluation of observed differences. [...]if this observation were repeated 100 times in similar populations of the same sample size, 95 of the sampled death rates would fall between .011 and .440. [...]in populations where disease prevalence is high, there will be greater confidence that a positive test result is a true positive, and increased suspicion that a negative test result is a false negative. Diagram of Observed Frequencies Extracted for Odds Ratio Example The relative risk or risk ratio (RR) is calculated from a cohort study where exposed and non-exposed participants are followed over time and the incidence of disease is observed. Because the hallmark of a cohort study is following a population over time to identify incident cases of disease, the cohort is screened to assure that no participant enrolled in the study has already experienced the outcome or disease event.