ratio hazard ratio A measure of association that is the ratio of the hazard rate of an event in one group to the hazard rate of the same event in another group. Brian S. Alper, Kenneth Wilkins, Joanne Dehnbostel, Muhammad Afzal Hazard rate is defined as: A conditional instantaneous rate in which the numerator represents an incidence conditioned on survival to a specified time, and the denominator represents a time interval with a duration approaching zero. The groups being compared are often the exposed group versus the unexposed group, but hazard ratio can also be applied to comparisons of one exposure relative to another exposure. A hazard ratio of one means there is no difference between two groups in terms of their hazard rates, based on whether or not they were exposed to a certain substance or factor, or how they responded to two interventions being compared. A hazard ratio of greater than one implies an association of greater risk, and a hazard ratio of less than one implies an association of lower risk. The hazard ratio can be calculated from studies in which the proportion of exposed participants who had the event is known, the proportion of unexposed participants who had the event is known, and the timing of events for each participant is known or estimable, such as a cohort study or clinical trial. NCIt: Hazard ratio = A measure of how often a particular event happens in one group compared to how often it happens in another group, over time. In cancer research, hazard ratios are often used in clinical trials to measure survival at any point in time in a group of patients who have been given a specific treatment compared to a control group given another treatment or a placebo. A hazard ratio of one means that there is no difference in survival between the two groups. A hazard ratio of greater than one or less than one means that survival was better in one of the groups. https://www.statisticshowto.com/hazard-ratio/ The hazard ratio is a comparison between the probability of events in a treatment group, compared to the probability of events in a control group. Hazard Ratio in Clinical Trials (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC478551/) The hazard ratio is an estimate of the ratio of the hazard rate in the treated versus the control group. The hazard rate is the probability that if the event in question has not already occurred, it will occur in the next time interval, divided by the length of that interval. The time interval is made very short, so that in effect the hazard rate represents an instantaneous rate. The Hazards of Hazard Ratios (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3653612/) The hazard ratio (HR) is the main, and often the only, effect measure reported in many epidemiologic studies. For dichotomous, non–time-varying exposures, the HR is defined as the hazard in the exposed groups divided by the hazard in the unexposed groups. For all practical purposes, hazards can be thought of as incidence rates and thus the HR can be roughly interpreted as the incidence rate ratio. The HR is commonly and conveniently estimated via a Cox proportional hazards model, which can include potential confounders as covariates. ready for release